Portrait of Dr Paul Saines

Dr Paul Saines

Senior Lecturer in Chemistry

About

Dr Paul Saines obtained a Bachelor of Science degree with first class honours from the University of Sydney, graduating with a university medal in 2004. He stayed at Sydney to carry out a PhD focusing on analysing phase transitions in perovskite oxides, under the supervision of Professor Brendan Kennedy, from which he graduated at the end of 2008 with the AINSE gold medal. 

Paul then spent periods as a postdoc at the University of Cambridge, focusing on the creation and characterisation of magnetic frameworks in the group of Professor Anthony Cheetham, and at the University of Oxford, working with Professor Andrew Goodwin on the local magnetic and crystallographic structure of ferrous oxide. In 2013 he was awarded a prestigious Glasstone Fellowship at Oxford to independently investigate the magnetic interactions in multiferroic and low dimensional frameworks. 

Paul joined the School of Physical Sciences at the University of Kent in late 2015 as a Lecturer in Chemistry and has since been awarded the Institute of Physics Physical Crystallography Prize.

Research interests

Materials with complex and tuneable electronic and magnetic interactions play a key role in the function of many modern technologies. Work in the Saines' group focuses on designing new co-ordination compounds, which form extended crystalline frameworks, as a novel route to developing substances with such functional properties. Such materials can adopt unusual architectures, controlled by the cations and organic ligands they incorporate, enable new routes or unusual modifications to their functions that cannot be found in conventional magnetic and electronic materials. The electronic and magnetic behaviour of these frameworks are intricately linked to their crystal structures and the group uses cutting-edge characterisation techniques to develop a deeper understanding of the key role of structure-property relationships in their properties. A particular strength of the Saines' group is determining how the atomic scale magnetic structure of such metal-organic frameworks affect their macroscopic properties.

Smart electronic and magnetic compounds

Memory storage and sensing applications require magnets with more complex and adjustable properties than traditional materials. This requires the development of new multiferroic materials, in which electronic and magnetic order are coupled, or relaxor ferroelectric whose polarisation properties are useful across a wider temperature range. Framework materials are ideal for these applications as they exhibit unique physical properties not observed in other magnets, owing to the role their cations and ligands play in shaping them. The ternary formates are an archetypal example of this. Their structures are comprised of a magnetically active B-site metal while the A-site is occupied by an organic cation that can order ferroelectrically; multiferroic behaviour arises from the host-guest interactions in these materials and their ferroelectric properties often resemble relaxors. Paul's group has recently established the effect of cation size on the architecture formed by such ternary formates, along with more detailed studies of the nature of their electronic and magnetic interactions. Current work includes exploring analogous ternary frameworks containing other organic cations and ligands as a route to improving the multiferroic properties of these compounds.

Low-dimensional frameworks

Materials with strong bonding or magnetic interactions in fewer than three dimensions can exhibit unusual physical properties. Frameworks are ideal low-dimensional materials as their structure can be readily tailored to feature isolated sheets or chains. Compounds with weak, non-covalent interactions in one or two dimensions are amenable for delamination into nano-sheets or chains, which can exhibit enhanced properties owing to their nanostructures. Magnets with low-dimensional interactions can also adopt exotic spin structures, providing tremendous insight into the fundamental nature of magnetism. The group's recent work has shown that low-dimensional magnetic frameworks have considerable potential as low-temperature coolants, and they are currently exploring routes for improving such materials further, underpinned by detailed studies of their magnetic interactions.

Teaching

Paul's teaching includes co-ordination complexes, electronic transitions and magnetism of the transition metals, lanthanides and actinides; methods for making functional solid materials; solids with functional magnetic and electronic properties; and X-ray powder diffraction.

Supervision

Paul regularly supervises undergraduate chemistry and physics research projects and the research projects of Master's and PhD students. These are typically in experimental solid state chemistry and condensed matter physics with a particular focus on materials with functional magnetic and electronic properties.

Professional


Publications

Showing 50 of 53 total publications in the Kent Academic Repository. View all publications.

Article

  • Dixey, R., Orlandi, F., Manuel, P., Mukherjee, P., Dutton, S. and Saines, P. (2019). Emergent Magnetic Order and Correlated Disorder in Formate Metal-organic Frameworks. Philosophical Transactions of the Royal Society A [Online] 337. Available at: http://dx.doi.org/10.1098/rsta.2019.0007.
    Magnetic materials with strong local interactions
    but lacking long-range order have long been
    a curiosity of physicists. Probing their magnetic
    interactions is crucial for understanding the unique
    properties they can exhibit. Metal-organic frameworks
    have recently gathered more attention as they
    can produce more exotic structures, allowing for
    controlled design of magnetic properties not found
    in conventional metal-oxide materials. Historically,
    magnetic diffuse scattering in such materials have
    been overlooked but has attracted greater attention
    recently, with advances in techniques. In this study
    we investigate the magnetic structure of metal-organic
    formate frameworks, using heat capacity, magnetic
    susceptibility and neutron diffraction. In Tb(DCO2)3
    we observe emergent magnetic order at temperatures
    below 1.2 K, consisting of two k-vectors. Ho(DCO2)3
    shows diffuse scattering above 1.6 K, consistent
    with ferromagnetic chains packed in a frustrated
    antiferromagnetic triangular lattice, also observed in
    Tb(DCO2)3 above 1.2 K. The other lanthanides show
    no short or long-range order down to 1.6 K. The results
    suggest an Ising-like 1D magnetic order associated
    with frustration is responsible for the magnetocaloric
    properties, of some members in this family, improving
    at higher temperatures.
  • Chalmers, J., Srivastava, A., Dixey, R., Sivakumaran, K. and Saines, P. (2019). Low Dimensional and Frustrated Antiferromagnetic Interactions in Transition Metal Chloride Complexes with Simple Amine Ligands. CrystEngComm [Online] 21:894-901. Available at: https://doi.org/10.1039/C8CE01901K.
    This study reports the facile synthesis, crystal structures and magnetic properties of five new Mn, Co and Cu complexes with chloride and simple amine ligands. The four hydrazinium complexes are discrete in nature while the O-methylhydroxylamine phase contains edge-sharing chains bridged by chloride ligands. Investigation of the magnetic properties of these materials reveals that two of these materials, Co(NH3NH2)2(H2O)2Cl4 and Cu(NH2OCH3)2Cl2, exhibit interesting antiferromagnetic properties arising from their low dimensional structures. Co(NH3NH2)2(H2O)2Cl4 appears to exhibit significant 2D magnetic frustration while the magnetic susceptibilities of Cu(NH2OCH3)2Cl2 are well fitted by a one-dimensional chain model. The relationship between the strength of the magnetic coupling observed in these materials and their likely exchange pathways are also discussed.
  • Tyuleva, S., Allen, N., White, L., Pepes, A., Shepherd, H., Saines, P., Ellaby, R., Mulvihill, D. and Hiscock, J. (2018). A Symbiotic Supramolecular Approach to the Design of Novel Amphiphiles with Antibacterial Properties Against MSRA. Chemical Communications [Online] 55. Available at: http://dx.doi.org/10.1039/C8CC08485H.
    Herein, we identify Supramolecular Self-associating Amphiphiles (SSAs) as a novel class of antibacterials with activity towards Methicillin-resistant Staphylococcus aureus. Structure-activity relationships have been identified in the solid, solution and gas phases. Finally, we show that when supplied in combination, SSAs exhibit increased antibacterial efficacy against these clinically relevant microbes.
  • Dixey, R. and Saines, P. (2018). Optimisation of the Magnetocaloric Effect in Low Applied Magnetic Fields in LnOHCO3 Frameworks. Inorganic Chemistry [Online] 57:12543-12551. Available at: http://dx.doi.org/10.1021/acs.inorgchem.8b01549.
    This study probes the structure and magnetocaloric effect of the LnOHCO3 (Ln = Gd3+, Tb3+, Dy3+, Ho3+ and Er3+) frameworks. A
    combination of single crystal X-ray and neutron powder diffraction indicate that these materials solely adopt the P212121 structure
    under these synthetic conditions and magnetic susceptibility measurements indicate they remain paramagnetic down to 2 K. We
    show that the magnetocaloric effect of TbOHCO3 and DyOHCO3 have a peak entropy change of 30.99 and 33.34 J Kg-1 K-1 for a 2-0 T field change respectively, which is higher than than the promising GdOHCO3 framework above 4 K in moderate magnetic
    fields. The magnetic entropy change of TbOHCO3 and DyOHCO3 above 4 K for sub-2T field changes also exceeds that of
    Gd3Ga5O12 and Dy3Ga5O12, making them suitable magnetic cooling materials for use at liquid helium temperatures using the low
    applied magnetic fields accessible using permanent magnets, advantageous for efficient practical cooling devices.
  • Saines, P. and Bristowe, N. (2018). Probing Magnetic Interactions in Metal-Organic Frameworks and Coordination Poylmers Microscopically. Dalton Transactions [Online]. Available at: https://doi.org/10.1039/C8DT02411A.
    Materials with magnetic interactions between their metal centres play both a tremedous role in modern technologies and can exhibit unique physical phenomena. In recent years magnetic metal-organic frameworks and coordination polymers have attracted significant attention because their unique structural flexibility enable them to exhibit multifunctional magnetic properties or unique magnetic states not found in conventional magnetic materials, such as metal oxides. The techniques that enable the magnetic interactions in these materials to be probed at the atomic scale, as long established as key for devloping other magnetic materials, are not well established for studying metal-organic frameworks and coordination polymers. This review focuses on studies where metal-organic frameworks and coordination polymers have been examined by such microscopic probes, with a particular focus on neutron scattering and density-functional theory, the most-well established experimental and computational techniques for understanding magnetic materials in detail. This builds on a brief introduction to these techniques to describe how such probes have been applied to a variety of magnetic materials starting with select historical examples before discussing multifunctional, low dimensional and frustrated magnets. This review highlight the information that can be obtained from such micrscopic studies, including the strengths and limitations of these techniques. The article then concludes with a brief perspective on the future of this area.
  • Gibbs, A., Yamamoto, A., Yaresko, A., Knight, K., Yasuoka, H., Majumder, M., Baenitz, M., Saines, P., Hester, J., Hashizume, D., Kondo, A., Kindo, K. and Takagi, H. (2017). S=12 quantum critical spin ladders produced by orbital ordering in Ba2CuTeO6. Physical Review B [Online] 95. Available at: https://doi.org/10.1103/PhysRevB.95.104428.
  • Bovill, S., Dixey, R. and Saines, P. (2017). Three Coordination Frameworks with Copper Formate based Low Dimensional Motifs: Synthesis, Structure and Magnetic Properties. CrystEngComm [Online] 19:1831-1838. Available at: http://dx.doi.org/10.1039/C6CE01601D.
    In this study we report the synthesis, crystal structures and magnetic properties of three frameworks wherein Cu cations are bridged by formate linkers into one-dimensional motifs. One of these compounds, Cu2(HCO2)3(C3N2H4)4(NO3), contains a ladder motif but remains paramagnetic to 2 K. This is likely because of the longer superexchange pathway along its chains due to the orientation of the Jahn-Teller axis of its Cu cations. In contrast Cu(HCO2)(NO3)(NH3)2 and Cu(HCO2)(ClO4)(NH3)2 feature Cu(HCO2) chains in which the Jahn-Teller axis is oriented perpendicular to the chain direction; these exhibit antiferromagnetic order below 12 and 7 K, respectively. Their magnetic susceptibilities are well fitted by a one-dimensional chain model but further examination of their magnetic properties reveals significant inter-chain magnetic coupling and a lack of spin dynamics. This suggests that these transitions correspond to the emergence of long-range magnetic order, highlighting the importance of detailed studies of frameworks containing low dimensional motifs to gain a deeper understanding of their magnetic behaviour.
  • Aston, J. and Saines, P. (2017). Transition-Metal Dependent Cation Disorder in the Chiral Cubic AB(HCO2)3 Metal-Organic Frameworks (A = Li or Na, B = Mn or Co). Zeitschrift fur Anorganische und Allgemeine Chemie [Online] 643:287-293. Available at: http://dx.doi.org/10.1002/zaac.201600350.
    This study examines the crystal structures of the AB(HCO2)3 (A = Li or Na and B = Mn or Co) metal-organic frameworks, which we find to adopt a chiral cubic P213 structure. This shows that the Li containing formates are isostructural with their Na analogues, extending the phase stability of this chiral architecture. The Mn containing compounds have a magnetic sublattice similar to ?-Mn, long of interest due to its highly frustrated antiferromagnetic coupling. In contrast the Co formates appear to have partially disordered alkali and transition metal cations, which prevents the formation of a clean ?-Mn-like magnetic sublattice. We have also re-examined the magnetic properties of NaMn(HCO2)3 finding it to be a simple paramagnet down to 2 K with only weak antiferromagnetic coupling.
  • Saines, P., Harcombe, D., Welch, P., Manuel, P. and Goodwin, A. (2016). One-dimensional magnetic order in the metal–organic framework Tb(HCOO)3. Physical Review B: Condensed Matter and Materials Physics [Online] 94. Available at: http://dx.doi.org/10.1103/PhysRevB.94.174429.
    Variable-temperature neutron scattering measurements, reverse Monte Carlo analysis and direct Monte Carlo simulation are used to characterise magnetic order in the metal–organic framework (MOF) Tb(HCOO)3 over the temperature range 100K to 1.6K = TN. The magnetic transition at TN is shown to involve one-dimensional ferromagnetic ordering to a partially-ordered state related to the triangular Ising antiferromagnet and distinct from the canonical “partially-disordered antiferromagnet” model. In this phase, the direction of magnetisation of ferromagnetic chains tends to alternate between neighbouring chains but this alternation is frustrated and is not itself ordered. We suggest the existence of low-dimensional magnetic order in Tb(HCOO)3 is stabilised by the contrasting strength of inter- and intra-chain magnetic coupling, itself a consequence of the underlying MOF architecture. Our results demonstrate how MOFs may provide an attractive if as yet under-explored platform for the realisation and investigation of low-dimensional physics.
  • Saines, P., Timm, L., Tucker, M., Keen, D., Thygesen, P. and Goodwin, A. (2016). Exploration of Antiferromagnetic CoO and NiO using Reverse Monte Carlo Total Neutron Scattering Refinement. Physica Scripta [Online] 91. Available at: http://dx.doi.org/10.1088/0031-8949/91/11/114004.
    The atomic and magnetic structures of CoO and NiO have been probed using reverse Monte Carlo refinements of neutron total scattering data. The results obtained show that the known magnetic structure for NiO can be recovered by the reverse Monte Carlo process starting from random spin configurations, but it is insensitive to the spin direction in the {111} ferromagnetic planes. Refinements of the magnetic structure of CoO starting from random spin configurations result in collinear or non-collinear magnetic structure, consistent with those reported by other techniques. Starting from an ordered collinear spin structure for CoO and NiO leads to different results than when starting from a random arrangement of spins, evidence for configurational bias that highlights the need to take care when selecting a starting model for reverse Monte Carlo refinements of magnetic structures.
  • Lawler, J., Manuel, P., Thompson, A. and Saines, P. (2015). Probing ferroic transitions in a multiferroic framework family: a neutron diffraction study of the ammonium transition metal formates. Dalton Transactions [Online] 44:11613-11620. Available at: http://dx.doi.org/10.1039/c5dt00733j.
    This study probes the magnetic and ferroelectric ordering of the NH<inf>4</inf>M(HCO<inf>2</inf>)<inf>3</inf> (M = Mn2+, Fe2+, Co2+ and Ni2+) frameworks using neutron diffraction, improving the understanding of the origins of the properties of these fascinating multiferroics. This rare study of the magnetic structure of a family of metal-organic frameworks shows that all four compounds exhibit antiferromagnetic coupling between neighbouring cations bridged by formate ligands. The orientation of the spin, however, changes in a highly unusual way across the series with the spins aligned along the c-axis for the Fe2+ and Ni2+ frameworks but lying in the ab plane for the other members of the series. This work also sheds new light on the nature of the ferroelectric order-disorder transition in these materials; probing changes in the ammonium cation across the transition and also shows that the Ni2+ framework does not undergo a transition to the polar P6<inf>3</inf> phase due to the smaller size of the Ni2+ cation. Finally trends in their anisotropic negative thermal expansion, which potentially enhances their ferroic behaviour, are quantified.
  • Yu, W., Cheung, Y., Saines, P., Imai, M., Matsumoto, T., Michioka, C., Yoshimura, K. and Goh, S. (2015). Strong Coupling Superconductivity in the Vicinity of the Structural Quantum Critical Point in (CaxSr1?x)3Rh4Sn13. Physical Review Letters: Moving Physics Forward [Online] 115:207003. Available at: http://dx.doi.org/10.1103/PhysRevLett.115.207003.
    The family of the superconducting quasiskutterudites (CaxSr1?x)3Rh4Sn13 features a structural quantum critical point at xc=0.9, around which a dome-shaped variation of the superconducting transition temperature Tc is found. Using specific heat, we probe the normal and the superconducting states of the entire series straddling the quantum critical point. Our analysis indicates a significant lowering of the effective Debye temperature on approaching xc, which we interpret as a result of phonon softening accompanying the structural instability. Furthermore, a remarkably large enhancement of 2?/kBTc and ?C/?Tc beyond the Bardeen-Cooper-Schrieffer values is found in the vicinity of the structural quantum critical point. The phase diagram of (CaxSr1?x)3Rh4Sn13 thus provides a model system to study the interplay between structural quantum criticality and strong electron-phonon coupling superconductivity.
  • Svane, K., Saines, P. and Walsh, A. (2015). Magnetoelastic coupling in the cobalt adipate metal-organic framework from quasi-harmonic lattice dynamics. Journal of Materials Chemistry C [Online] 3:11076-11080. Available at: http://dx.doi.org/10.1039/C5TC02633D.
    Magnetic interactions in hybrid materials are poorly understood compared to those in purely inorganic materials. The high flexibility of many metal-organic systems introduces a strong temperature dependence of the magnetic exchange interactions owing to changes in the crystal structure. Here, we study the cobalt adipate system, for which anisotropic thermal expansion was recently shown to be a result of magnetoelastic coupling. The combination of density functional theory with quasi-harmonic lattice dynamics is shown to be a powerful tool for describing temperature dependent thermodynamic potentials that determine magnetic interactions. It is demonstrated that the effect of phonons can be sufficient to switch the preference for ferromagnetic versus antiferromagnetic ordering.
  • Bovill, S. and Saines, P. (2015). Structure and magnetic properties of the AB(HCO2)3 (A = Rb+ or Cs+, B = Mn2+, Co2+ or Ni2+) frameworks: probing the effect of size on the phase evolution of the ternary formates. CrystEngComm [Online] 17:8319-8326. Available at: http://dx.doi.org/10.1039/C5CE01628B.
    This work reports the synthesis and structures of six new AB(HCO2)3 (A = Rb+ or Cs+ and B = Mn2+, Co2+ or Ni2+) frameworks containing the largest monoatomic cations on the A-site. RbMn(HCO2)3 is found to adopt a distorted perovskite framework with a 412[middle dot]63 topology and a mixture of syn-anti and anti-anti ligands, while the remaining compounds adopt a chiral hexagonal structure with a 49[middle dot]66 topology. The structures of these frameworks clarify the effect of ionic size on the formation of the five known architectures adopted by the AB(HCO2)3 frameworks, which have attracted attention as a new class of potential multiferroics, and in particular the chiral hexagonal structure within this. This also highlights the role of molecular A-site cations in stabilising the 49[middle dot]66 topology for frameworks where such cations are too large or small to support this structure on the basis of size alone, possibly due to hydrogen bonding. The magnetic properties of the RbB(HCO2)3 and CsMn(HCO2)3 frameworks are also reported with the Rb+ compounds featuring weak ferromagnetic behaviour and the latter being purely antiferromagnetic. In conjunction with a comparison of the other isostructural AB(HCO2)3 frameworks we find that compounds adopting the 49[middle dot]66 topology have much higher magnetic ordering temperatures than those with the RbMn(HCO2)3 structure, highlighting the importance of understanding the structure-property relationships of the ternary formates.
  • Komuro, N., Mikami, M., Saines, P., Akimoto, K. and Cheetham, A. (2015). Deep red emission in Eu2+-activated Sr4(PO4)2O phosphors for blue-pumped white LEDs. Journal of Materials Chemistry C [Online] 3:7356-7362. Available at: http://www.dx.doi.org/10.1039/c5tc01151e.
    he deep red phosphor Sr4(PO4)2O:Eu2+, which has an excitation peak around 450 nm for blue LED applications, is reported. This behavior is unusual for most phosphate phosphors. The crystal structure of Sr4(PO4)2O:Eu2+ is found to be monoclinic P21 and isotypic with Ca4(PO4)2O:Eu2+, which also shows deep red emission. Sr4(PO4)2O:Eu2+ has a larger lattice volume than Ca4(PO4)2O:Eu2+, but their emission and excitation spectra at room temperature are very similar. The key factors are discussed for achieving a large redshift of the 5d levels of Eu2+ ion in order to emit red light. In particular, the importance of the anion polarizability and the distortions of the metal coordination polyhedra are discussed, including the effective coordination number. Importantly, Sr4(PO4)2O:Eu2+ lacks the yellow emission at 77 K, which is found in Ca4(PO4)2O:Eu2+. The differences in thermal quenching behavior for Eu2+ dopants in Sr4(PO4)2O:Eu2+ and Ca4(PO4)2O:Eu2+ are attributed to the degree of auto/photo-ionization due to differences in the band gaps of these compounds. The importance of the large band gap of the host lattice in avoiding non-radiative processes of energy relaxation was confirmed.
  • Saines, P., Paddison, J., Thygesen, P. and Tucker, M. (2015). Searching beyond Gd for magnetocaloric frameworks: magnetic properties and interactions of the Ln(HCO2)3 series. Materials Horizons [Online] 2:528-535. Available at: http://dx.doi.org/10.1039/c5mh00113g.
    This study probes the magnetic properties and interactions of the Ln(HCO<inf>2</inf>)<inf>3</inf> (Ln = Tb3+-Er3+) frameworks. We show that the magnetocaloric effect of Tb(HCO<inf>2</inf>)<inf>3</inf> is significantly higher above 4 K in moderate magnetic fields compared to the promising Gd(HCO<inf>2</inf>)<inf>3</inf>. While the peak performance of Tb(HCO<inf>2</inf>)<inf>3</inf> is lower than Gd(HCO<inf>2</inf>)<inf>3</inf>, we also find that the Gd-rich members of the solid solution Gd<inf>1-x</inf>Tb<inf>x</inf>(HCO<inf>2</inf>)<inf>3</inf> blend the advantages of both end-members. Using neutron diffraction experiments, Tb(HCO<inf>2</inf>)<inf>3</inf> is found to be antiferromagnetic below 1.7 K with ferromagnetic face-sharing chains and antiferromagnetic coupling between them. Analysis of magnetic diffuse scattering of the paramagnetic phase indicates that ferromagnetic coupling is retained, and it is likely that this plays a role in improving its magnetocaloric performance in low fields. This journal is © The Royal Society of Chemistry.
  • Goh, S., Tompsett, D., Saines, P., Chang, H., Matsumoto, T., Imai, M., Yoshimura, K. and Grosche, F. (2015). Ambient pressure structural quantum critical point in the phase diagram of (CaxSr1-x)3Rh4Sn13. Physical Review Letters: Moving Physics Forward [Online] 114. Available at: http://dx.doi.org/10.1103/PhysRevLett.114.097002.
    The quasiskutterudite superconductor Sr3Rh4Sn13 features a pronounced anomaly in electrical resistivity at T??138K. We show that the anomaly is caused by a second-order structural transition, which can be tuned to 0 K by applying physical pressure and chemical pressure via the substitution of Ca for Sr. A broad superconducting dome is centered around the structural quantum critical point. Detailed analysis of the tuning parameter dependence of T? as well as insights from lattice dynamics calculations strongly support the existence of a structural quantum critical point at ambient pressure when the fraction of Ca is 0.9 (i.e., xc=0.9). This establishes the (CaxSr1-x)3Rh4Sn13 series as an important system for exploring the physics of structural quantum criticality without the need of applying high pressures.
  • Komuro, N., Mikami, M., Saines, P. and Cheetham, A. (2015). Structure-property correlations in Eu-doped tetra calcium phosphate phosphor: A key to solid-state lighting application. Journal of Luminescence [Online] 162:25-30. Available at: http://dx.doi.org/10.1016/j.jlumin.2015.02.006.
    The unique emission characteristics and the crystal structure of Ca4(PO4)2O:Eu2+ were studied. Considerably broad emission from 500 nm to 800 nm was measured at 77 K when the material was excited at 365 nm. Its crystal structure was refined using neutron diffraction, allowing precise and accurate oxygen positions to be determined. This enabled a relationship between the optical properties and the crystal structure crucial for achieving a large redshift of the 5d level of Eu2+ to be established, which is important to match the excitation energy band with near-ultraviolet or blue light-emitting-diodes used for solid-state lighting. The importance of the anion polarizability and the distortion of the coordination polyhedron were also discussed.
  • Saines, P., Barton, P., Jura, M., Knight, K. and Cheetham, A. (2014). Cobalt adipate, Co(C6H8O4): antiferromagnetic structure, unusual thermal expansion and magnetoelastic coupling. Materials Horizons [Online] 1:332-337. Available at: http://doi.org/10.1039/C4MH00009A.
    Co adipate, Co(C6H8O4), has been found to order near 10 K into a magnetic structure featuring sheets of tetrahedral Co cations coupled antiferromagnetically in two dimensions through carboxylate groups. The emergence of this order is accompanied by magnetoelastic coupling, which drives anisotropic negative thermal expansion along the a-axis below 50 K, the first time such behaviour has been observed in a metal-organic framework. The monoclinic angle, beta, has also been found to decrease on cooling, passing through a metrically orthorhombic phase without a phase transition; this unusual behaviour has been rationalised in terms of the thermal expansion along the principal axes.
  • Kalaji, A., Saines, P., George, N. and Cheetham, A. (2013). Photoluminescence of cerium-doped (Ca1-xSrx) 3RE2Ge3O12 garnet phosphors for solid state lighting: Relating structure to emission. Chemical Physics Letters [Online] 586:91-96. Available at: http://dx.doi.org/10.1016/j.cplett.2013.09.007.
    A novel family of cerium-doped garnet oxide phosphors, (Ca 1-xSrx)3RE2Ge3O 12:Ce,Li (2%, 2%) (x=0-1, RE = Y, Lu), was prepared using a conventional high-temperature ceramic route and was found to exhibit green luminescence under blue excitation. These compounds were characterised by synchrotron X-ray diffraction and photoluminescence spectroscopy. The results from this study were compared with other known Ce-doped garnets, including yttrium aluminium garnet, leading to a deeper understanding of the relationship between crystal structure and emission wavelength. In particular, the relationship between Ce3+ emission and the distortion factor of the dodecahedral doping site (d88/d81) was examined.
  • Saines, P., Steinmann, M., Tan, J., Yeung, H. and Cheetham, A. (2013). Structural diversity and luminescent properties of lanthanide 2,2- and 2,3-dimethylsuccinate frameworks. CrystEngComm [Online] 15:100-110. Available at: http://dx.doi.org/10.1039/c2ce26279g.
    The structures of fourteen new lanthanide frameworks (La, Ce, Eu, Tb, Y and Lu) containing the 2,2- or 2,3-dimethylsuccinate ligands are reported. While the majority of the known 2,2-dimethylsuccinate frameworks feature two dimensionally bonded layers, capped by hydrophobic methyl groups, several of these new frameworks adopt quite different architectures. These include one dimensional inorganically connected chains (La and Ce) with only non-covalent interactions in the other two dimensions, and three dimensional covalently bonded frameworks (Eu and Lu) with spaces in their structure to accommodate the bulky methyl groups. The new 2,3-dimethylsuccinate frameworks (La and Y) adopt three-dimensional covalently bonded frameworks. The factors affecting the formation of structures with different dimensionalities are examined and compared to previously reported transition metal frameworks. In addition, the sequence of phases formed with changing lanthanide size, concentrations and temperatures are rationalised. The luminescent properties of several 1- and 2-D frameworks doped with Eu and Tb are reported, with the Y host exhibiting the most intense emission.
  • Yeung, H., Li, W., Saines, P., Koster, T., Grey, C. and Cheetham, A. (2013). Ligand-directed control over crystal structures of inorganic-organic frameworks and formation of solid solutions. Angewandte Chemie International Edition [Online] 52:5544-5547. Available at: http://dx.doi.org/10.1002/anie.201300440.
    Grounded in fact: Inorganic-organic frameworks with 3D Li-O-Li connectivity can form solid solutions through mechanochemical synthesis. High-resolution synchrotron powder X-ray diffraction and cross-polarization solid-state NMR spectroscopy demonstrate complete ligand mixing in the resulting binary and ternary systems (see picture for trends in unit cell volume (V) of the ternary system {Li2(suc)x(mal)y(met)z} n).
  • Bennett, T., Saines, P., Keen, D., Tan, J. and Cheetham, A. (2013). Ball-milling-induced amorphization of zeolitic imidazolate frameworks (ZIFs) for the irreversible trapping of iodine. Chemistry - A European Journal [Online] 19:7049-7055. Available at: http://dx.doi.org/10.1002/chem.201300216.
    The I2-sorption and -retention properties of several existing zeolitic imidazolate frameworks (ZIF-4, -8, -69) and a novel framework, ZIF-mnIm ([Zn(mnIm)2]; mnIm=4-methyl-5-nitroimidazolate), have been characterised using microanalysis, thermogravimetric analysis and X-ray diffraction. The topologically identical ZIF-8 ([Zn(mIm)2]; mIm=2-methylimidazolate) and ZIF-mnIm display similar sorption abilities, though strikingly different guest-retention behaviour upon heating. We discover that this guest retention is greatly enhanced upon facile amorphisation by ball milling, particularly in the case of ZIF-mnIm, for which I2 loss is retarded by as much as 200 °C. It is anticipated that this general approach should be applicable to the wide range of available metal-organic framework-type materials for the permanent storage of harmful guest species.
  • Li, W., Zhang, Z., Bithell, E., Batsanov, A., Barton, P., Saines, P., Jain, P., Howard, C., Carpenter, M. and Cheetham, A. (2013). Ferroelasticity in a metal-organic framework perovskite; Towards a new class of multiferroics. Acta Materialia [Online] 61:4928-4938. Available at: http://dx.doi.org/10.1016/j.actamat.2013.04.054.
    A metal-organic framework perovskite, [(CH2)3NH 2][Mn(HCOO)3], exhibits a weakly first order ferroelastic phase transition at ?272 K, from orthorhombic Pnma to monoclinic P2 1/n, and a further transition associated with antiferromagnetic ordering at ?8.5 K. The main structural changes, through the phase transition, are orientational ordering of the azetidium groups and associated changes in hydrogen bonding. In marked contrast to conventional improper ferroelastic oxide perovskites, the driving mechanism is associated with the X-point of the cubic Brillouin zone rather than being driven by R- and M-point octahedral tilting. The total ferroelastic shear strain of up to ?5% is substantially greater than found for typical oxide perovskites, and highlights the potential of the flexible framework to undergo large relaxations in response to local structural changes. Measurements of elastic and anelastic properties by resonant ultrasound spectroscopy show some of the characteristic features of ferroelastic materials. In particular, acoustic dissipation below the transition point can be understood in terms of mobility of twin walls under the influence of external stress with relaxation times on the order of ?10-7 s. Elastic softening as the transition is approached from above is interpreted in terms of coupling between acoustic modes and dynamic local ordering of the azetidium groups. Subsequent stiffening with further temperature reduction is interpreted in terms of classical strain-order parameter coupling at an improper ferroelastic transition which is close to being tricritical. By way of contrast, there are no overt changes in elastic or anelastic properties near 9 K, implying that any coupling of the antiferromagnetic order parameter with strain is weak or negligible.
  • Saines, P., Tucker, M., Keen, D., Cheetham, A. and Goodwin, A. (2013). Coupling of the local defect and magnetic structure of wüstite Fe 1-xO. Physical Review B - Condensed Matter and Materials Physics [Online] 88. Available at: http://dx.doi.org/10.1103/PhysRevB.88.134418.
    The local nuclear and magnetic structure of wüstite, Fe 1-xO, and the coupling between them, have been examined using reverse Monte Carlo refinements of variable-temperature neutron total scattering data. The results from this analysis suggest that the individual units in a tetrahedral defect cluster are connected along 〈110â Œ vectors into a Koch-Cohen-like arrangement, with the majority of octahedral vacancies concentrated near these defects. Bond valence calculations indicate a change in the charge distribution on the cations with the charge on the tetrahedral interstitials increasing on cooling. The magnetic structure is more complex than previously thought, corresponding to a noncollinear spin arrangement described by a superposition of a condensed spin wave on the established type-II antiferromagnetic ordering. This leads to an architecture with four groups of cations, each with different spin directions. The cations within the interstitial clusters appear to be weakly ferromagnetically coupled, and their spins are correlated to the spins of the octahedral cations closest to them. This work not only provides further insight into the local structure of wüstite but also enables a better understanding of the coupling between defect structures and magnetic and charge ordering in complex materials.
  • Saines, P., Barton, P., Jain, P. and Cheetham, A. (2012). Structures and magnetic properties of Mn and Co inorganic-organic frameworks with mixed linear dicarboxylate ligands. CrystEngComm [Online] 14:2711-2720. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-84860271222&partnerID=40&md5=cf72fb98d6b24bf3ceed7f7f9e879809.
    The structures and magnetic properties of two transition metal frameworks that feature a mixture of two linear dicarboxylate ligands are reported. Compounds 1, Mn 2(C 4H 4O 4)(C 6H 8O 4)(H 2O) 4· 2H 2O, and 2, Co 6(C 4H 4O 4) 4(C 6H 8O 4)(OH) 2(H 2O) 4·5H 2O, contain a mixture of succinate and adipate ligands but adopt significantly different structures. Compound 1 features layers of MnO 6 dimers, intra-connected by carboxylate groups, with neighbouring dimers connected to each other via the adipate ligands in one direction and succinate ligands in the other. Extensive hydrogen bonding in the third dimension provides the main force holding layers together. Framework 2 has inorganic layers of CoO 6 octahedra arranged into rings of 14 members each, with adipate ligands providing inter-layer connectivity. The structures of these two compounds are compared to Mn and Co dicarboxylate frameworks containing only one type of organic ligand, including Co(C 6H 8O 4), compound 3, whose structure is reported in this work for the first time; they are found to be significantly different from those that form under similar conditions. Both compounds order magnetically near 2 K. Compound 1 is an antiferromagnet, in which the intra-dimer coupling dominates the magnetic behaviour, while framework 2 is most likely a canted antiferromagnet. Both compounds undergo magnetic phase transitions with increasing applied magnetic fields, at 14 kOe and 0.35 kOe in 1 and 2, respectively. The transition in the Mn compound is a simple spin flop but in the Co compound the suppression of the long range ordered state is also accompanied by the elimination of the ferromagnetic component of its magnetic interactions. © 2012 The Royal Society of Chemistry.
  • Saines, P., Steinmann, M., Tan, J., Yeung, H., Li, W., Barton, P. and Cheetham, A. (2012). Isomer-directed structural diversity and its effect on the nanosheet exfoliation and magnetic properties of 2,3-dimethylsuccinate hybrid frameworks. Inorganic Chemistry [Online] 51:11198-11209. Available at: http://dx.doi.org/10.1021/ic302011x.
    The structures of seven new transition metal frameworks featuring Mn, Co, or Zn and either the meso or chiral d and l isomers of the 2,3-dimethylsuccinate ligand are reported. Frameworks that exhibit two-dimensional covalently bonded layers with weak interlayer interactions can be made with all three cations by incorporation of the chiral isomers of the 2,3-dimethylsuccinate ligand. The formation of such structures, suitable for the creation of nanosheets via exfoliation, is, however, not as ubiquitous as is the case with the 2,2-dimethylsuccinate frameworks since frameworks that incorporate the meso-2,3-dimethylsuccinate ligand form three-dimensional structures. This clear distinction between the formation of structures with covalent connectivity in two and three dimensions, depending on the choice of 2,3-dimethylsuccinate isomer, is due to the different conformations adopted by the backbone of the ligand. The chiral isomer prefers to adopt an arrangement with its methyl and carboxylate groups gauche to the neighboring functional groups of the same type, while the meso-ligand prefers to adopt trans geometry. A gauche-arrangement of the methyl groups places them on the same side of the ligand, making this geometry ideal for the formation of layered structures; a trans-relationship leads to the methyl groups being further apart, reducing their steric hindrance and making it easier to accommodate them within a three-dimensional structure. The ease of exfoliation of the layered frameworks is examined and compared to those of known transition metal 2,2-dimethylsuccinate frameworks by means of UV-vis spectroscopy. It is suggested that layered frameworks with more corrugated surfaces exfoliate more rapidly. The size, structure, and morphology of the exfoliated nanosheets are also characterized. The magnetic properties of the paramagnetic frameworks reveal that only the three dimensionally covalently bonded phases containing meso-2,3-DMS in trans-arrangements order magnetically. These frameworks are antiferromagnets at low temperatures, although the Co compound undergoes an unusual antiferromagnetic to ferromagnetic transition with increasing applied magnetic field.
  • Klintberg, L., Goh, S., Alireza, P., Saines, P., Tompsett, D., Logg, P., Yang, J., Chen, B., Yoshimura, K. and Grosche, F. (2012). Pressure- and composition-induced structural quantum phase transition in the cubic superconductor (Sr,Ca)3Ir4Sn13. Physical Review Letters [Online] 109. Available at: http://dx.doi.org/10.1103/PhysRevLett.109.237008.
    We show that the quasi-skutterudite superconductor Sr3Ir 4Sn13 undergoes a structural transition from a simple cubic parent structure, the I phase, to a superlattice variant, the I ? phase, which has a lattice parameter twice that of the high temperature phase. We argue that the superlattice distortion is associated with a charge density wave transition of the conduction electron system and demonstrate that the superlattice transition temperature T* can be suppressed to zero by combining chemical and physical pressure. This enables the first comprehensive investigation of a superlattice quantum phase transition and its interplay with superconductivity in a cubic charge density wave system.
  • Tan, J., Saines, P., Bithell, E. and Cheetham, A. (2012). Hybrid nanosheets of an inorganic-organic framework material: Facile synthesis, structure, and elastic properties. ACS Nano [Online] 6:615-621. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-84856168218&partnerID=40&md5=37d47fb1539f10df7311de75528abda4.
    Figure Persented: We report a new 2-D inorganic-organic framework material, MnDMS [Mn 2,2-dimethylsuccinate], featuring weakly bound hybrid layers in its bulk crystals that can be readily exfoliated into nanosheets via ultrasonication. The fully exfoliated hybrid nanosheets correspond to a unilamellar thickness of about 1 nm, while the partially exfoliated nanosheets (multilayer films) exhibit a typical thickness on the order of 10 nm. We used atomic force microscopy to characterize their surface topography and to map the variation of nanomechanical properties across the surface of the delaminated nanosheets. The morphology and crystallographic orientation of the exfoliated layers were further studied by transmission electron microscopy. Additionally, we investigated the elastic anisotropy underlying the bulk host material by means of single-crystal nanoindentation, from which the critical resolved shear stress (Ï? crit) needed for the micromechanical delamination of individual layers was determined to be relatively small (â?²0.4 GPa). © 2011 American Chemical Society.
  • Zhang, Z., Church, N., Lappe, S., Reinecker, M., Fuith, A., Saines, P., Harrison, R., Schranz, W. and Carpenter, M. (2012). Elastic and anelastic anomalies associated with the antiferromagnetic ordering transition in wüstite, Fe xO. Journal of Physics Condensed Matter [Online] 24:953-953. Available at: http://dx.doi.org/10.1088/0953-8984/24/21/215404.
    The elastic and anelastic properties of three different samples of Fe xO have been determined in the frequency range 0.12MHz by resonant ultrasound spectroscopy and in the range 0.150Hz by dynamic mechanical analysis in order to characterize ferroelastic aspects of the magnetic ordering transition at T N195K. No evidence was found of separate structural and magnetic transitions but softening of the shear modulus was consistent with the involvement of bilinear coupling, λe 4q, between a symmetry-breaking strain, e 4, and a structural order parameter, q. Unlike a purely ferroelastic transition, however, C 44 does not go to zero at the critical temperature" due to the intervention of the magnetic ordering at a higher temperature. The overall pattern of behaviour is nevertheless consistent with what would be expected for a system with separate structural and magnetic instabilities, linearquadratic coupling between the structural (q) and magnetic (m) driving order parameters, ?qm 2, and . Comparison with data from the literature appears to confirm the same pattern in MnO and NiO, with a smaller difference between T N and in the former and a larger difference in the latter. Strong attenuation of acoustic resonances at high frequencies and a familiar pattern of attenuation at low frequencies suggest that twin walls in the rhombohedral phase have typical ferroelastic properties. Acoustic dissipation in the stability field of the cubic phase is tentatively attributed to anelastic relaxations of the defect ordered structure of non-stoichiometric wüstite or of the interface between local regions of wüstite and magnetite, with a rate controlling step determined by the diffusion of iron.
  • Saines, P., Tan, J., Yeung, H., Barton, P. and Cheetham, A. (2012). Layered inorganic-organic frameworks based on the 2,2-dimethylsuccinate ligand: Structural diversity and its effect on nanosheet exfoliation and magnetic properties. Dalton Transactions [Online] 41:8585-8593. Available at: http://dx.doi.org/10.1039/c2dt30648d.
    The structures of four new 2,2-dimethylsuccinate frameworks suitable for exfoliation into nanosheets using ultrasonication are reported. These hybrid compounds contain either monovalent (Li +) or divalent (Co 2+ and Zn 2+) cations, and they all feature hydrophobically capped covalently bonded layers that only interact with each other via weak van der Waals forces. Critically this shows that the use of this dicarboxylate ligand generally yields two dimensional compounds suitable for simple and affordable nanosheet exfoliation. This extends the range of frameworks that can be exfoliated and highlights the 2,2-dimethylsuccinate ligand as an excellent versatile platform for the production of nanosheets. The topologies of the layers in each framework were found to vary significantly and this appears to have a significant effect on the relative size of the nanosheets produced; increased space between methyl groups and more extensive inorganic connectivity appears to favour the formation of thin nanosheets with larger lateral dimensions. Additionally the magnetic properties of two of these frameworks were examined, and it was found that both exhibit strong low dimensional antiferromagnetic coupling despite their well-separated layers preventing three dimensional magnetic order.
  • Webster, N., Hartlieb, K., Saines, P., Ling, C. and Lincoln, F. (2011). New quenched-in fluorite-type materials in the Bi2O 3-La2O3-PbO system: Synthesis and complex phase behaviour up to 750 °c. Materials Research Bulletin [Online] 46:538-542. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-79952185734&partnerID=40&md5=5d95cdd35f8e5ed91caf1c8f4b57f4bd.
    New quenched-in fluorite-type materials with composition (BiO 1.5)0.94-x(LaO1.5)0.06(PbO) x, x = 0.02, 0.03, 0.04 and 0.05, were synthesised by solid state reaction. The new materials undergo a number of phase transformations during heating between room temperature and 750 °C, as indicated by differential thermal analysis. Variable temperature X-ray diffraction performed on the material (BiO1.5)0.92(LaO1.5) 0.06(PbO)0.02 revealed that the quenched-in fcc fluorite-type material first undergoes a transformation to a β-Bi 2O3-type tetragonal phase around 400 °C. In the range 450-700 °C, α-Bi2O3-type monoclinic, Bi 12PbO19-type bcc and β1/β 2-type rhombohedral phases, and what appeared to be a ε-type monoclinic phase, were observed, before a single-phase fluorite-type material was regained at 750 °C. © 2010 Elsevier Ltd © 2011 Elsevier Ltd. All rights reserved.
  • Saines, P., Yeung, H., Hester, J., Lennie, A. and Cheetham, A. (2011). Detailed investigations of phase transitions and magnetic structure in Fe(iii), Mn(ii), Co(ii) and Ni(ii) 3,4,5-trihydroxybenzoate (gallate) dihydrates by neutron and X-ray diffraction. Dalton Transactions [Online] 40:6401-6410. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-79958810464&partnerID=40&md5=d12689345c49b6fe4c8d7c7d036d7d27.
    The effect of cation valency on the complex structures of divalent and trivalent transition metal gallates has been examined using a combination of neutron and synchrotron X-ray powder diffraction, single-crystal X-ray diffraction and XANES spectroscopy. In the divalent frameworks, M(C 7H4O5)·2H2O (M = Mn, Co and Ni), it was found that charge balance was achieved via the presence of protons on the meta-hydroxyl groups. It was also established that these compounds undergo a discontinuous phase transition at lower temperatures, which is driven by the position of the extra-framework water molecules in these materials. By contrast, in the trivalent Fe gallate, Fe(C7H3O 5)·2H2O, it was found that the stronger bonding between the meta-hydroxy oxygen and the cations leads to a weakening of the bond between this oxygen and its proton. This is turn is thought to lead to stronger hydrogen bonding with the extra-framework water. The lattice water is disordered in the Fe(iii) case, which prevents the phase transition found in the M(ii) gallates. Refinement against the neutron diffraction patterns also revealed that the relatively mild microwave synthesis of gallate frameworks in D2O led to an extensive deuteration of the ortho-hydrogen sites on the aromatic ring, which may suggest a more versatile method of deuterating aromatic organics. The antiferromagnetic structure of Co gallate has also been determined. © 2011 The Royal Society of Chemistry.
  • Saines, P., Jain, P. and Cheetham, A. (2011). Evolution of the structures and magnetic properties of the manganese dicarboxylates, Mn2(CO2(CH2)nCO 2)(OH)2 and Mn4(CO2(CH 2)nCO2)3(OH)2. Chemical Science [Online] 2:1929-1939. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-81355133859&partnerID=40&md5=736dd857a67aeaa938ef87ec0a4f5f2c.
    Two new series of basic Mn dicarboxylate frameworks, Mn2(CO 2(CH2)nCO2)(OH)2 (where n = 0, 2, 4 and 5) and Mn4(CO2(CH2) nCO2)3(OH)2 (where n = 3 and 5), have been synthesised and the evolution of their structures with changing length of the dicarboxylate ligand was examined. Compounds in the Mn 2(CO2(CH2)nCO2)(OH) 2 series contain 2 dimensionally inorganically connected layers, which are bridged in the third dimension by the dicarboxylate ligand. While the compounds in this series with n = 0 or 2 contain only octahedrally coordinated Mn, the frameworks with longer ligands, n = 4 or 5, have a 1:1 ratio of octahedrally and trigonal bipyramidally coordinated cations. Structures in the Mn4(CO2(CH2)nCO2) 3(OH)2 series contain inorganically connected double chains of MnOx polyhedra, which comprise an equal number of octahedra and trigonal bipyramids. Trigonal bipyramidal coordination environments are very rarely found in dicarboxylate frameworks and the roles of the longer dicarboxylate ligands and the d5 electronic configuration of Mn 2+ in their formation are discussed. The magnetic properties of Mn2(CO2(CH2)2CO2)(OH) 2 have also been examined. It undergoes two magnetic transitions. The higher temperature transition to a two dimensionally ordered antiferromagnetic phase occurs around 44 K, in low applied fields, and is followed by a transition to a three dimensionally ordered canted antiferromagnetic state near 36 K. The Néel temperature of this phase is unusually high for a transition metal dicarboxylate and the factors thought to support this are examined. © The Royal Society of Chemistry 2011.
  • Saines, P., Melot, B., Seshadri, R. and Cheetham, A. (2010). Synthesis, structure and magnetic phase transitions of the manganese succinate hybrid framework, Mn(C4H4O4). Chemistry - A European Journal [Online] 16:7579-7585. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-77954082105&partnerID=40&md5=d3d4fec45e49456056c3a154c961d6f9.
    An anhydrous manganese succinate, Mn(C4H4O 4), has been synthesised hydrothermally and studied by single-crystal X-ray diffraction. It adopts a succinate pillared structure in which layers of corner-sharing MnO6 octahedra alternate with sheets that contain chains of edge-sharing octahedra. This unique 3D framework structure contains highly distorted MnO6 octahedra, which are made possible by the lack of ligand field stabilisation energy for the high-spin Mn2+ ion. Attempts to dope the structure with other divalent transition-metal ions were accordingly unsuccessful. Magnetic sus-ceptibility and heat capacity measurements indicate that Mn(C4H4O4) undergoes antiferromagnetic ordering below 12 K, with a second antiferromagnetic transition at approximately 6 K. These two antiferromagnetic phases undergo further transitions in applied fields, underlining the subtle magnetic behaviour that is possible in inorganic-organic frameworks of this structural complexity. © 2010 Wiley-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.
  • Saines, P., Hester, J. and Cheetham, A. (2010). Neutron diffraction study of the magnetic structures of manganese succinate Mn(C4H4O4): A complex inorganic-organic framework. Physical Review B - Condensed Matter and Materials Physics [Online] 82:0-0. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-78049453256&partnerID=40&md5=d34e8327c753f023eaed5f5f721261b5.
    The antiferromagnetic structures of the Mn succinate framework, Mn(C 4H4O4), have been determined using neutron diffraction. The structure comprises alternating layers containing chains of edge-sharing Mn (II) O6 octahedra and sheets of corner-sharing Mn (II) O6 octahedra, respectively, with a layer separation of �7.5. At 10 K the edge-sharing MnO6 octahedral chains order antiferromagnetically into a collinear sinusoidal spin structure with a propagation vector k2 = (0,-0.5225,0), in which individual edge-sharing MnO6 chains are ferromagnetically ordered. The sheets of corner-sharing MnO6 octahedra order magnetically at 6 K, adopting the antiferromagnetic structure expected for a square arrangement of cations with a propagation vector k8 = (-1,0,1). The ordering of these sheets at a lower temperature than the chains is consistent with their longer nearest-neighbor superexchange pathway. The magnetic structure of the edge-sharing layers is unaffected by the 6 K phase transition, indicating that the orderings of the two different layers are essentially independent of each other. © 2010 The American Physical Society.
  • Saines, P., Kennedy, B. and Smith, R. (2009). Structural phase transitions in BaPrO3. Materials Research Bulletin [Online] 44:874-879. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-59849105961&partnerID=40&md5=a6545e864c2e88071ae07ba130c700b5.
    The crystal structures adopted by BaPrO3 at and above ambient temperature have been examined using a combination of synchrotron X-ray and neutron diffraction. BaPrO3 has been established to undergo a series of phase transitions from P b n m orthorhombic â?? I b m m orthorhombic â?? R over(3, Ì?) c rhombohedral â?? P m over(3, Ì?) m cubic. BaPrO3 is the second A2+B4+O3 perovskite found to adopt rhombohedral symmetry in preference to the I4/mcm tetragonal structure. Analysis of the octahedral tilting through the rhombohedral to cubic phase transition indicates that this transformation is continuous and tricritical in nature. The tricritical behaviour of this transition is likely to be a result of the competition between tetragonal and rhombohedral structures to be the preferred phase, with the rhombohedral symmetry adopted by BaPrO3 being stabilised by the unusually large B-site cation. © 2008 Elsevier Ltd. All rights reserved.
  • Kennedy, B., Saines, P., Ting, J., Zhou, Q. and Kimpton, J. (2009). Structural characterisation of the perovskite series SrxCa1-x-yNdyMnO3: Influence of the Jahn-Teller effect. Journal of Solid State Chemistry [Online] 182:2858-2866. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-70349558078&partnerID=40&md5=ce7ccd53e7856f6bbc86d71321a12a5f.
    The crystal structures of the perovskite manganites SrxCa1-x-yNdyMnO3 with y=0.1 or 0.2 have been investigated using synchrotron X-ray powder diffraction. At room temperature the structures change from Pm over(3, -) m â?? I 4 / mcm â?? Pbnm depending on the cation distribution, the different structures exhibiting different tilts of the MnO6 octahedra. High temperature diffraction measurements demonstrate the presence of, an apparently continuous, isosymmetric I4/mcm to I4/mcm phase transition associated with the removal of long range orbital ordering. Heating the manganites to still higher temperatures results in a continuous transition to the cubic Pm over(3, -) m structure. A feature of such transitions is the continuous evolution of the octahedral tilt angle through the I4/mcm to I4/mcm phase transition. The orthorhombic structures do not exhibit orbital ordering and although a first order transition to the tetragonal structure is observed in Sr0.4Ca0.5Nd0.1MnO3, this high temperature tetragonal structure does not exhibit orbital ordering. © 2009 Elsevier Inc. All rights reserved.
  • Saines, P., Kennedy, B., Johannessen, B. and Poulton, S. (2008). Phase and valence transitions in Ba2LnSnxNb1-xO6-δ. Journal of Solid State Chemistry [Online] 181:2994-3004. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-55549088535&partnerID=40&md5=24410ab6ed2c4e03d9ed00baf0c90e0d.
    The structures of compounds in the perovskite series Ba2LnSnxNb1-xO6-δ (Ln=Pr and Tb and x=0, 0.1, 0.2, ..., 1.0) have been examined using synchrotron X-ray and neutron diffraction. It was found that niobate members of both series feature full B-site cation ordering but that this order is lost with increasing x. X-ray absorption near-edge structure (XANES) and near-infrared spectroscopies indicate that the oxidation state of the lanthanide cations gradually changes from Ln3+ to Ln4+ with increased Sn4+ doping. This is believed to be the cause of the loss of B-site ordering. Least squares analysis of the XANES spectra suggests that the rate of the transformation of Ln3+ cations to the tetravalent state is such that the Pr series contains no oxygen vacancies while the Tb series may contain a very small amount of vacancies, with δâ??0.02. © 2008 Elsevier Inc. All rights reserved.
  • Thorogood, G., Saines, P., Kennedy, B., Withers, R. and Elcombe, M. (2008). Diffuse scattering in the cesium pyrochlore CsTi0.5W1.5O6. Materials Research Bulletin [Online] 43:787-795. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-39649108649&partnerID=40&md5=e6966e3e352982978f370f24ae53c406.
    The structure of the defect pyrochlore CsTi0.5W1.5O6 has been investigated using electron, synchrotron X-ray and neutron diffraction methods. The material is cubic a = 10.2773 Ã? with displacive disorder of the Cs cations along the ã??1 1 1ã?? direction. The local structure, revealed by the diffuse structure in the electron diffraction patterns shows there is correlated displacement of the heavy Cs atoms along the ã??1 1 0ã?? directions. The thermal expansion of the material is also described. © 2008 Elsevier Ltd. All rights reserved.
  • Saines, P. and Kennedy, B. (2008). Phase segregation in mixed Nb-Sb double perovskites Ba2LnNb1-xSbxO6. Journal of Solid State Chemistry [Online] 181:298-305. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-38649120853&partnerID=40&md5=cac07651280d96e42125af43fd1f6d5a.
    The phase composition of two series of mixed Nb5+-Sb5+ double perovskites formed between the pairs Ba2EuNbO6-Ba2PrSbO6 and Ba2NdSbO6-Ba2NdNbO6 have been studied using synchrotron X-ray powder diffraction methods. In both series extensive phase segregation is observed demonstrating limited solubility of Sb5+ in these Nb5+ perovskites, irrespective of the precise structures of the double perovskite. Evidence for a monoclinic I2/m phase in the series formed between tetragonal I4/m Ba2EuNbO6 and rhombohedral R over(3, -) Ba2EuNbO6 is presented. It is postulated that this phase segregation is a consequence of competing bonding requirements of the Nb5+ and Sb5+ cations associated with their electronic configurations. © 2007 Elsevier Inc. All rights reserved.
  • Larsson, A., Withers, R., Perez-Mato, J., Fitz Gerald, J., Saines, P., Kennedy, B. and Liu, Y. (2008). On the microstructure and symmetry of apparently hexagonal BaAl2O4. Journal of Solid State Chemistry [Online] 181:1816-1823. Available at: https://doi.org/10.1016/j.jssc.2008.03.043.
    The P63 (a=2ap, b=2bp, c=cp) crystal structure reported for BaAl2O4 at room temperature has been carefully re-investigated by a combined transmission electron microscopy and neutron powder diffraction study. It is shown that the poor fit of this P63 (a=2ap, b=2bp, c=cp) structure model for BaAl2O4 to neutron powder diffraction data is primarily due to the failure to take into account coherent scattering between different domains related by enantiomorphic twinning of the P6322 parent sub-structure. Fast Fourier transformation of [0 0 1] lattice images from small localized real space regions (�10 nm in diameter) are used to show that the P63 (a=2ap, b=2bp, c=cp) crystal structure reported for BaAl2O4 is not correct on the local scale. The correct local symmetry of the very small nano-domains is most likely orthorhombic or monoclinic. © 2008 Elsevier Inc. All rights reserved.
  • Kennedy, B., Saines, P., Zhou, Q., Zhang, Z., Matsuda, M. and Miyake, M. (2008). Structural and electronic phase transitions in Sr1-xCe xMnO3 perovskites. Journal of Solid State Chemistry [Online] 181:2639-2645. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-55349090985&partnerID=40&md5=6f6fb519bf21b6b063d2541d29f35e8c.
    The structures of eight members of the series Sr1-xCe xMnO3 with 0.075â?¤xâ?¤0.4 have been established using synchrotron X-ray powder diffraction. These exhibit the sequence of structures cubic/Pm3Ì?m xâ??0.08/â?? tetragonal/14/mcm xâ??0.35/rarr; orthorhombic/Imma with increasing Ce content. Unusual peak broadening due to domainwall scattering is observed near the composition-induced first-order cubic-tetragonal transition. The temperature dependence of the structures for three examples x = 0.1, 0.2 and 0.35 is described. For the x = 0.1 and 0.35 samples evidence for a first-order loss of the orbital ordering associated with a cooperative Jahn-Teller distortion is presented. The onset of the orbitally disordered state is accompanied by a discontinuous reduction in cell volume. © 2008 Elsevier Inc. All rights reserved.
  • Saines, P., Kennedy, B., Elcombe, M., Harris, H., Jang, L. and Zhang, Z. (2008). Phase and valence transitions in Ba2LnSnxSb1-xO6-δ (Ln=Pr and Tb). Journal of Solid State Chemistry [Online] 181:2941-2952. Available at: https://doi.org/10.1016/j.jssc.2008.07.007.
    Compounds in the double perovskites series Ba2LnSnxSb1-xO6-δ (Ln=Pr and Tb) have been synthesised and structurally characterised using synchrotron X-ray and neutron powder diffraction. It was found that the two end-members of the Ba2PrSnxSb1-xO6-δ series both adopt rhombohedral symmetry but the antimonate is a fully ordered double perovskite while the stannate has no B-site cation ordering. X-ray absorption near-edge structure (XANES) and near-infrared spectroscopy indicate that the Pr cations gradually change oxidation state from Pr3+ to Pr4+ with increasing x and that this is likely to be the cause of the loss of B-site ordering. Similarly, both Ba2TbSbO6 and Ba2TbSnO6-δ are cubic with B-site ordering present in the former but absent in the latter due to the oxidation state change of the Tb from Tb3+ to Tb4+. Multiple linear regression analysis of the Pr and Tb LIII-edge XANES indicates that the rate of Ln3+ transforming to Ln4+ is such that there are no oxygen vacancies in Ba2PrSnxSb1-xO6-δ but in Ba2TbSnxSb1-xO6-δ there is a small amount of oxygen vacancies, with a maximum of δâ??0.05 present. Crown Copyright © 2008.
  • Zhou, Q., Saines, P., Sharma, N., Ting, J., Kennedy, B., Zhang, Z., Withers, R. and Wallwork, K. (2008). Crystal structures and phase transitions in a-site deficient perovskites Ln1/3TaO3. Chemistry of Materials [Online] 20:6666-6676. Available at: https://doi.org/10.1021/cm8014868.
    The synthesis and structures of the perovskites Ln1/3TaO 3 are described. As the size of the Ln cation is reduced, the compounds display a sequence of structure: P4/mmm/La â?? Cmmm/Ce-Gd â?? Pmma/Tb, Dy â?? Pmc21/Ho, Er. Although apparently tetragonal in P4/mmm, electron diffraction patterns of Tm1/3TaO3 reveal this has a complex incommensurate structure. Likewise Gd1/3TaO 3 appears metrically tetragonal, but electron diffraction and synchrotron X-ray powder diffraction demonstrate this is actually orthorhombic. The suppression of the spontaneous orthorhombic strain in Gd 1/3TaO3 is thought to be due to the proximity to the first-order Cmmm-Pmma transition. Variable temperature studies show both Tb 1/3TaO3 and Dy1/3TaO3 undergo a first-order Cmmm-Pmma transition upon heating. © 2008 American Chemical Society.
  • Saines, P., Spencer, J., Kennedy, B. and Avdeev, M. (2007). Structures and crystal chemistry of the double perovskites Ba2LnBâ?²O6 (Ln=lanthanide Bâ?²=Nb5+ and Ta5+): Part I. Investigation of Ba2LnTaO6 using synchrotron X-ray and neutron powder diffraction. Journal of Solid State Chemistry [Online] 180:2991-3000. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-36148991066&partnerID=40&md5=2feb3962ec126eb3b0526408f2e73dce.
    The structure of 14 compounds in the series Ba2LnTaO6 have been examined using synchrotron X-ray diffraction and found to undergo a sequence of phase transitions from I2/m monoclinic to I4/m tetragonal to Fm over(3, -) m cubic symmetry with decreasing ionic radii of the lanthanides. Ba2LaTaO6 is an exception to this with variable temperature neutron diffraction being used to establish that the full series of phases adopted over the range of 15-500 K is P21/n monoclinic to I2/m monoclinic to R over(3, -) rhombohedral. The chemical environments of these compounds have also been investigated and the overbonding to the lanthanide cations is due to the unusually large size for the B-site in these perovskites. © 2007 Elsevier Inc. All rights reserved.
  • Saines, P., Spencer, J., Kennedy, B., Kubota, Y., Minakata, C., Hano, H., Kato, K. and Takata, M. (2007). Structures and crystal chemistry of the double perovskites Ba2LnBâ?²O6 (Ln=lanthanide and Bâ?²=Nb, Ta):. Part II-Temperature dependence of the structures of Ba2LnBâ?²O6. Journal of Solid State Chemistry [Online] 180:3001-3007. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-36148995893&partnerID=40&md5=465a6657026e60107657aa7954b94f82.
    The structures of eight members of the series of double perovskites of the type Ba2LnB�O6 (Ln=La3+-Sm3+ and Y3+ and B�=Nb5+ and Ta5+) were examined both above and below room temperature using synchrotron X-ray powder diffraction. The La3+ and Pr3+ containing compounds had an intermediate rhombohedral phase whereas the other tantalates and niobates studied have a tetragonal intermediate. This difference in symmetry appears to be a consequence of the larger size of the La3+ and Pr3+ cations compared to the other lanthanides. The temperature range over which the intermediate symmetry is stable is reduced in those compounds near the point where the preferred intermediate symmetry changes from tetragonal to rhombohedral. In such compounds the transition to the cubic phase involves higher order terms in the Landau expression. This suggests that in this region the stability of the two intermediate phases is similar. © 2007 Elsevier Inc. All rights reserved.
  • Kennedy, B., Saines, P., Kubota, Y., Minakata, C., Hano, H., Kato, K. and Takata, M. (2007). Crystal structures and phase transitions in Ba2HoTaO6. Materials Research Bulletin [Online] 42:1875-1880. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-34548385381&partnerID=40&md5=22c0aa51efc86f55c6bbdc529655d36a.
    The structure of the cation-ordered double perovskite Ba2HoTaO6 was examined using synchrotron X-ray powder diffraction at fine temperature intervals over the range of 90-300 K. Ba2HoTaO6 has a cubic structure in space group F m over(3, Ì?) m at room temperature. A proper ferroelastic phase transition to I4/m tetragonal symmetry occurs near approximately 260 K. Analysis of the spontaneous tetragonal strain versus temperature indicated that the phase transition is second order in nature. © 2007 Elsevier Ltd. All rights reserved.
  • Saines, P., Kennedy, B. and Elcombe, M. (2007). Structural phase transitions and crystal chemistry of the series Ba2LnBâ?²O6 (Ln=lanthanide and Bâ?²=Nb5+ or Sb5+). Journal of Solid State Chemistry [Online] 180:401-409. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-33846561489&partnerID=40&md5=80c90e0f1bf49f0f78eb6443d69c141e.
    The structures of 28 compounds in the two series Ba2LnSbO6 and Ba2LnNbO6 have been examined using synchrotron X-ray and in selected cases neutron powder diffraction at, below and above ambient temperature. The antimonate series is found to undergo a sequence of phase transitions from monoclinic to rhombohedral to cubic symmetry with both decreasing ionic radii of the lanthanides and increasing temperature. Compounds in the series Ba2LnNbO6, on the other hand, feature an intermediate tetragonal structure instead of the rhombohedral structure exhibited by the antimonates. This difference in symmetry is thought to be caused by Ï?-bonding in the niobates that is absent in the antimonates. The bonding environments of the cations in these compounds have also been examined with overbonding of the lanthanide and niobium cations being caused by the unusually large B-site cations. © 2006 Elsevier Inc. All rights reserved.
  • Saines, P., Elcombe, M. and Kennedy, B. (2006). Lanthanide distribution in some doped alkaline earth aluminates and gallates. Journal of Solid State Chemistry [Online] 179:613-622. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-33344456809&partnerID=40&md5=a2c215c1bb0266d28ace5cb4043bab6a.
    High-resolution neutron and synchrotron X-ray powder diffraction studies are reported for the six oxides AB2O4 (A=Ca2+, Sr2+ and Ba2+ and B=Al3+ and Ga3+). These oxides all adopt a stuffed tridymite type structure, the precise nature of which depends on both the A- and B-type cations. Bond valence calculations reveal a range of values for the various A-type cations, in all cases at least one site is significantly underbonded. Conversely the tetrahedral B-type sites invariably exhibit unexceptional bond valencies. Attempts to dope the oxides with various lanthanides to the 1% level invariably resulted in some segregation into alternate phases located at the grain boundaries. The identity of the impurity phases is presented and the importance of bond valencies in understanding this segregation is highlighted.
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