Portrait of Dr Emma McCabe

Dr Emma McCabe

Senior Lecturer in Chemistry
Deputy Director of Undergraduate Studies for Chemistry Stages 2-4 and Employability
Academic Lead for Industrial Placements
Radiation Protection Officer
Deputy Research Group Leader

About

Emma obtained a first class honours degree in MNatSc (Chemistry) at the University of Birmingham. She stayed in Birmingham to carry out research for a PhD (2006) on layered, perovskite-related materials with Professor Colin Greaves, for which she was awarded the Challinor prize.  She then took up a PDRA position at the University of Sheffield in Professor Tony West’s group, where she worked on a range of materials, before moving to Durham University to work on mixed anion systems as a PDRA with Professor John S. O. Evans. 

Emma was appointed Lecturer in Chemistry at the University of Kent in January 2013 (and Senior Lecturer in 2015) and is a member of the Functional Materials Group in the School of Physical Sciences.  She is a member of the Solid State Group of the Royal Society of Chemistry, and of the Physical Crystallography Group of the British Crystallographic Association, and serves on several international panels for diffraction.

Research interests

Dr McCabe's research interests lie in the field of materials chemistry and focus on the synthesis, structural characterisation and physical properties of complex transition metal oxides and mixed anion systems. Her areas of expertise include inorganic chemistry synthesis, magnetism in solids, structural characterisation and crystallography. Emma's interest in crystallography is driven by the structure-property relationship and understanding how changes in the composition and structure can be used to tune the physical properties of materials. 

Understanding multiferroic materials 

Materials that show long-range magnetic order or long-range ordering of electric dipoles are important research areas due to their applications in data storage devices, including read heads in computer hard drives. Materials that exhibit several ferroic orders are named 'multiferroics' and if these ferroic orders can be coupled, the potential for data storage applications is exciting, making this a key research topic in condensed matter science. This work is carried out in part through collaborations, including with groups in Belgium and in Sheffield.

Mixed anion transition metal systems 

Studies on transition metal (TM) oxides have been extremely fruitful but the importance of mixed anion systems has been highlighted recently by the discovery of high temperature iron-based superconductivity in oxyarsenide materials, and of copper oxychalcogenides which are transparent semiconductors. Emma's proposed work builds on existing knowledge of TM materials and applies this to develop new functional mixed anion materials which will fall into one of two categories: new magnetic TM systems, and new semiconducting materials.

Teaching

Emma currently teaches across the chemistry programmes; she also teaches on modules shared with the forensic science programmes.

Publications

Article

  • Chen, K., Di Paola, C., Laricchia, S., Reece, M., Weber, C., McCabe, E., Abrahams, I. and Bonini, N. (2020). Structural and electronic evolution in the Cu3SbS4–Cu3SnS4 solid solution. Journal of Materials Chemistry C [Online]. Available at: https://dx.doi.org/10.1039/D0TC01804J.
    Cu3Sb1−xSnxS4 samples with 0.0 ≤ x ≤ 1.0 were synthesized from pure elements by mechanical alloying combined with spark plasma sintering. The structural and electronic properties of these compounds were characterized by powder X-ray and neutron diffraction, X-ray photoelectron spectroscopy (XPS), magnetic susceptibility and electrical and thermal transport measurements, and the experimental results compared against those calculated from hybrid density functional theory. A full solid solution is found between famatinite (Cu3SbS4) and kuramite (Cu3SnS4), with low x-value compositions in the Cu3Sb1−xSnxS4 system exhibiting the ordered famatinite structure and compositions above x = 0.7 showing progressive disorder on the cation sublattice. The semiconducting behaviour of Cu3SbS4 becomes increasingly more metallic and paramagnetic with increasing Sn content as holes are introduced into the system. Neutron diffraction data confirm that the sulfur stoichiometry is maintained, while XPS results show Cu remains in the monovalent oxidation state throughout, suggesting that hole carriers are delocalized in the metallic band structure. The order–disorder transition is discussed in terms of the defect chemistry and the propensity towards disorder in these compounds.
  • Vera Stimpson, L., McNulty, J., Morrison, F., Mahajan, A., McCabe, E., Gibbs, A., Stenning, G., Jura, M. and Arnold, D. (2020). A comprehensive variable temperature study of the layered oxide, Ca2Mn3O8. Journal of Alloys and Compounds [Online]. Available at: https://doi.org/10.1016/j.jallcom.2020.155633.
    Ca2Mn3O8 forms a delafossite-related layered structure, which crystallises with monoclinic C2/m symmetry. Compared with the delafossite-structure, the MnO6 layers in Ca2Mn3O8 exhibit an ordered cation void which forms a magnetic ‘bow-tie’ like connectivity of Mn4+ ion layers separated by Ca2+ ions. In-situ variable temperature diffraction data demonstrates that the structure is robust up to a temperature of approximately 1173 K before the material decomposes into the perovskite, CaMnO3 and marokite, CaMn2O4 phases. Simultaneous thermal analysis suggests that a very small amount of water remains within the layers post synthesis. Impedance spectroscopy indicates that Ca2Mn3O8 is an electronic conductor in the range ∼400–700 K with an activation energy of 0.50 ± 0.01 eV.
  • Skiadopoulou, S., Retuerto, M., Borodavka, F., Kadlec, C., Kadlec, F., Míšek, M., Prokleška, J., Deng, Z., Tan, X., Frank, C., Alonso, J., Fernandez-Diaz, M., Croft, M., Orlandi, F., Manuel, P., McCabe, E., Legut, D., Greenblatt, M. and Kamba, S. (2020). Structural, magnetic, and spin dynamical properties of the polar antiferromagnets Ni3−xCoxTeO6(x=1,2). Physical Review B [Online] 101. Available at: https://doi.org/10.1103/PhysRevB.101.014429.
    We present results of a multimethod investigation of the polar antiferromagnets N i 2 CoTe O 6 and NiC o 2 Te O 6 , inspired by the colossal magnetoelectric effect present in N i 3 Te O 6 . Both compounds crystalize in the same polar space group R 3 as N i 3 Te O 6 , preserving the crystal symmetry at least from room temperature down to 2 K. N i 2 CoTe O 6 and NiC o 2 Te O 6 undergo antiferromagnetic phase transitions at T N = 55 and 52 K, and spin-flop transitions at an external magnetic field of approximately 8 and 4 T, respectively. Both compounds present an incommensurate antiferromagnetic helical structure with spins lying in the a b plane, in contrast to the collinear one along the c axis in N i 3 Te O 6 . Moreover, dielectric anomalies are observed at their antiferromagnetic phase transitions, suggesting a magnetoelectric behavior. Spin and lattice dynamics studies by a combination of infrared, Raman, and terahertz spectroscopies were performed. Below T N , in both N i 2 CoTe O 6 and NiC o 2 Te O 6 , low-frequency spin excitations extremely sensitive to external magnetic field were observed. At least one of these magnons was simultaneously seen in Raman and THz spectra of both compounds, therefore we propose to assign them to electromagnons.
  • Coles, B., Hillier, A., Coomer, F., Bristowe, N., Ramos, S. and McCabe, E. (2019). Spin interactions and magnetic order in the iron oxychalcogenides BaFe2Q2O(Q=Sand Se). Physical Review B [Online] 100:24427. Available at: https://doi.org/10.1103/PhysRevB.100.024427.
    The ability to tune the iron chalcogenides BaFe2Q3 from Mott insulators to metals and then superconductors with applied pressure has renewed interest in low-dimensional iron chalcogenides and oxychalcogenides. We report here a combined experimental and theoretical study on the iron oxychalcogenides BaFe2Q2O (Q = S, Se) and show that their magnetic behavior results from nearest-neighbor magnetic exchange interactions via oxide and selenide anions of similar strength, with properties consistent with more localized electronic structures than those of BaFe2Q3 systems.
  • Frank, C., McCabe, E., Orlandi, F., Manuel, P., Tan, X., Deng, Z., Croft, M., Cascos, V., Emge, T., Feng, H., Lapidus, S., Jin, C., Wu, M., Li, M., Ehrlich, S., Khalid, S., Quackenbush, N., Yu, S., Walker, D. and Greenblatt, M. (2019). Mn2CoReO6: A Robust Multisublattice Antiferromagnetic Perovskite with Small A-Site Cations. Chemical Communications [Online] 23. Available at: https://doi.org/10.1039/C9CC00038K.
    Mn2CoReO6, the fourth known magnetic transition-metal-only double perovskite oxide (space group P21/n) was synthesized at high pressure and temperature (8 GPa, 1350 ?C). Large structural distortions are induced by the small A-site Mn2+ cations. Mn2CoReO6 exhibits complex magnetic properties with a robust antiferromagentic order (TN = 94 K) involving all the cation sublattices .
  • Beqiri, D., Cascos- Jiménez, V., Roberts-Watts, J., Clark, E., Bousquet, E., Bristowe, N. and McCabe, E. (2019). Tuning octahedral tilts and the polar nature of A-site deficient perovskites. Chemical Communications [Online] 55:2609-2612. Available at: http://dx.doi.org/10.1039/C8CC10126D.
    Herein we highlight the ability to tune the structural chemistry of A-site deficient perovskite materials Ln1/3NbO3. Computational studies explore the balance between proper and hybrid-improper mechanisms for polar behaviour in these systems.
  • Tan, X., McCabe, E., Orlandi, F., Manuel, P., Batuk, M., Hadermann, J., Deng, Z., Jin, C., Nowik, I., Herber, R., Segre, C., Liu, S., Croft, M., Kang, C., Lapidus, S., Frank, C., Padmanabhan, H., Gopalan, V., Wu, M., Li, M., Greenblatt, M., Kotliar, G. and Walker, D. (2018). MnFe0.5Ru0.5O3: An Above-Room-Temperature Antiferromagnetic Semiconductor. Journal of Materials Chemistry C [Online]:509-522. Available at: https://doi.org/10.1039/c8tc05059g.
    A transition-metal-only MnFe0.5Ru0.5O3 polycrystalline oxide was prepared by a reaction of starting materials MnO, MnO2, Fe2O3, RuO2 at 6 GPa and 1873 K for 30 minutes. A combination of X-ray and neutron powder diffraction refinements indicated that MnFe0.5Ru0.5O3 adopts the corundum (a-Fe2O3) structure type with space group R3 @#x0305;c, in which all metal ions are disordered. The centrosymmetric nature of the MnFe0.5Ru0.5O3 structure is corroborated by transmission electron microscopy, lack of optical second harmonic generation, X-ray absorption near edge spectroscopy, and Mössbauer spectroscopy. X-ray absorption near edge spectroscopy of MnFe0.5Ru0.5O3 showed the oxidation states of Mn, Fe, and Ru to be 2+/3+, 3+, and ~4+, respectively. Resistivity measurements revealed that MnFe0.5Ru0.5O3 is a semiconductor. Magnetic measurements and magnetic structure refinements indicated that MnFe0.5Ru0.5O3 orders antiferromagnetically around 400 K, with magnetic moments slightly canted away from the c axis. 57Fe Mössbauer confirmed the magnetic ordering and Fe3+ (S = 5/2) magnetic hyperfine splitting. First principles calculations are provided to understand the electronic structure more thoroughly. A comparison of synthesis and properties of MnFe0.5Ru0.5O3 and related corundum Mn2BB'O6 derivatives is discussed.
  • Li, M., McCabe, E., Stephens, P., Croft, M., Collins, L., Kalinin, S., Deng, Z., Retuerto, M., Sen Gupta, A., Padmanabhan, H., Gopalan, V., Grams, C., Hemberger, J., Orlandi, F., Manuel, P., Li, W., Jin, C., Walker, D. and Greenblatt, M. (2017). Magnetostriction-polarization coupling in multiferroic Mn2MnWO6. Nature Communications [Online] 8. Available at: https://doi.org/10.1038/s41467-017-02003-3.
    Double corundum-related polar magnets are promising materials for multiferroic and magnetoelectric applications in spintronics. However, their design and synthesis is a challenge, and magnetoelectric coupling has only been observed in Ni3TeO6 among the known double corundum compounds to date. Here we address the high-pressure synthesis of a new polar and antiferromagnetic corundum derivative Mn2MnWO6, which adopts the Ni3TeO6-type structure with low temperature first-order field-induced metamagnetic phase transitions (TN?=?58?K) and high spontaneous polarization (~ 63.3 ?C·cm?2). The magnetostriction-polarization coupling in Mn2MnWO6 is evidenced by second harmonic generation effect, and corroborated by magnetic-field-dependent pyroresponse behavior, which together with the magnetic-field-dependent polarization and dielectric measurements, qualitatively indicate magnetoelectric coupling. Piezoresponse force microscopy imaging and spectroscopy studies on Mn2MnWO6 show switchable polarization, which motivates further exploration on magnetoelectric effect in single crystal/thin film specimens.
  • Oogarah, R., Suard, E. and McCabe, E. (2017). Magnetic order and phase transition in the iron oxysulfide La2O2Fe2OS2. Journal of Magnetism and Magnetic Materials [Online] 446:101-107. Available at: https://doi.org/10.1016/j.jmmm.2017.09.024.
    The Mott-insulating iron oxychalcogenides exhibit complex magnetic behaviour and we report here a neutron diffraction investigation into the magnetic ordering in La2O2Fe2OS2. This quaternary oxysulfide adopts the anti-Sr2MnO2Mn2Sb2-type structure (described by space group I4/mmm) and orders antiferromagnetically below TN = 105 K. We consider both its long-range magnetic structure and its magnetic microstructure, and the onset of magnetic order. It adopts the multi-k vector “2k” magnetic structure (k = (½ 0 ½) and k = (0 ½ ½) and has similarities with related iron oxychalcogenides, illustrating the robust nature of the “2k” magnetic structure.
  • Oogarah, R., Stockdale, C., Stock, C., Evans, J., Wills, A., Taylor, J. and McCabe, E. (2017). Crystal field excitations and magnons: their roles in oxyselenides Pr2O2M2OSe2 (M = Mn, Fe). Physical Review B [Online] 95. Available at: https://doi.org/10.1103/PhysRevB.95.174441.
  • McCabe, E. and Stock, C. (2016). The magnetic and electronic properties of oxyselenides—influence of transition metal ions and lanthanides. Journal of Physics: Condensed Matter [Online] 28. Available at: http://dx.doi.org/10.1088/0953-8984/28/45/453001.
    Magnetic oxyselenides have been a topic of research for several decades, firstly in the context of photoconductivity and thermoelectricity owing to their intrinsic semiconducting properties and ability to tune the energy gap through metal ion substitution. More recently, interest in the oxyselenides has experienced a resurgence owing to the possible relation to strongly correlated phenomena given the fact that many oxyselenides share a similar structure to unconventional superconducting pnictides and chalcogenides. The two dimensional nature of many oxyselenide systems also draws an analogy to cuprate physics where a strong interplay between unconventional electronic phases and localised magnetism has been studied for several decades. It is therefore timely to review the physics of the oxyselenides in the context of the broader field of strongly correlated magnetism and electronic phenomena. Here we review the current status and progress in this area of research with the focus on the influence of lanthanides and transition metal ions on the intertwined magnetic and electronic properties of oxyselenides. The emphasis of the review is on the magnetic properties and comparisons are made with iron based pnictide and chalcogenide systems.
  • McCabe, E., Bousquet, E., Stockdale, C., Deacon, C., Tran, T., Halasyamani, P., Stennett, M. and Hyatt, N. (2015). Proper Ferroelectricity in the Dion?Jacobson Material CsBi2Ti2NbO10: Experiment and Theory. Chemistry of Materials [Online] 27:8298-8309. Available at: http://dx.doi.org/10.1021/acs.chemmater.5b03564.
    A diverse range of materials and properties are exhibited by layered perovskites. We report on the synthesis, characterization, and computational investigation of a new ferroelectric?CsBi2Ti2NbO10, an n = 3 member of the Dion?Jacobson (DJ) family. Structural studies using variable temperature neutron powder diffraction indicate that a combination of octahedral rotations and polar displacements result in the polar structure. Density functional theory calculations reveal that the wider perovskite blocks in CsBi2Ti2NbO0 stabilize proper ferroelectricity, in contrast to the hybrid-improper ferroelectricity reported for all other DJ phases. Our results raise the possibility of a new class of proper ferroelectric materials analogous to the well-known Aurivillius phases.
  • Ainsworth, C., Wang, C., Johnston, H., McCabe, E., Tucker, M., Brand, H. and Evans, J. (2015). Infinitely Adaptive Transition-Metal Ordering in Ln2O2MSe2?Type Oxychalcogenides. Inorganic Chemistry [Online] 54:7230-7238. Available at: http://dx.doi.org/10.1021/acs.inorgchem.5b00599.
    A number of Ln2O2MSe2 (Ln = La and Ce; M = Fe, Zn, Mn,
    and Cd) compounds, built from alternating layers of fluorite-like [Ln2O2]2+
    sheets and antifluorite-like [MSe2]2? sheets, have recently been reported in the
    literatures. The available MSe4/2 tetrahedral sites are half-occupied, and
    different compositions display different ordering patterns: [MSe2]2? layers
    contain MSe4/2 tetrahedra that are exclusively edge-sharing (stripe-like),
    exclusively corner-sharing (checkerboard-like), or mixtures of both. This paper
    reports 60 new compositions in this family. We reveal that the transition-metal
    arrangement can be systematically controlled by either Ln or M doping, leading
    to an “infinitely adaptive” structural family. We show how this is achieved in
    La2O2Fe1 ? xZnxSe2, La2
    O2Zn1 ? xMnxSe2, La2
    O2Mn1 ? xCdxSe2 ,
    Ce2O2Fe1 ?xZnxSe2, Ce2
    O2Zn1?xMnxSe2, Ce2
    O2Mn1 ?xCdxSe2 ,
    La2?yCeyO2FeSe2, La2?yCeyO2ZnSe2, La2?yCeyO2MnSe2, and La2?yCeyO2CdSe2
    solid solutions.
  • Wang, C., Ainsworth, C., Gui, D., McCabe, E., Tucker, M., Evans, I. and Evans, J. (2015). Infinitely Adaptive Transition Metal Oxychalcogenides: The Modulated Structures of Ce2O2MnSe2 and (Ce0.78La0.22)2O2MnSe2. Chemistry of Materials [Online] 27:3121-3134. Available at: http://dx.doi.org/10.1021/acs.chemmater.5b00666.
    This article reports the syntheses, structures, and physical properties of the oxychalcogenides (Ce1–xLax)2O2MnSe2 with x = 0–0.7. These materials have a layered structure related to that of the LaOFeAs-derived superconductors but with the transition metal sites 50% occupied. Ce2O2MnSe2 contains alternating layers of composition: [Ce2O2]2+ and [MnSe2]2–. The size mismatch between the layers leads to an incommensurate structure with a modulation vector of q = ?a*+ 0b*+0.5c* with ? = 0.158(1), which can be described with a (3 + 1)D superspace structural model in superspace group Cmme(?,0,1/2)0s0 [67.12]. There is a strong modulation of Mn site occupancies, leading to a mixture of corner- and edge-sharing MnSe4/2 tetrahedra in the [MnSe2]2– layers. The modulation vector can be controlled by partial substitution of Ce3+ for larger La3+, and a simple commensurate case was obtained for (Ce0.78La0.22)2O2MnSe2 with ? = 1/6. The materials respond to the change in relative size of the oxide and chalcogenide blocks by varying the ratio of corner- to edge-sharing tetrahedra. The superspace model lets us unify the structural description of the five different ordering patterns reported to date for different Ln2O2MSe2 (Ln = lanthanide) materials. Mn moments in Ce2O2MnSe2 and (Ce0.78La0.22)2O2MnSe2 order antiferromagnetically below TN = 150 K, and Ce moments order below ?70 K. The magnetic structures of both materials have been determined using neutron diffraction. Both materials are semiconductors; Ce2O2MnSe2 has ? = 9 × 10–6 ?–1 cm–1 at room temperature and an activation energy for charge carrier mobility from RT to 170 °C of ?0.4 eV.
  • McCabe, E., Stock, C., Rodriguez, E., Wills, A., Taylor, J. and Evans, J. (2014). Weak spin interactions in Mott insulating La2O2Fe2OSe2. Physical Review B [Online] 89:100402-1. Available at: http://dx.doi.org/10.1103/PhysRevB.89.100402.
    Identifying and characterizing the parent phases of iron-based superconductors is an important step towards
    understanding the mechanism for their high-temperature superconductivity. We present an investigation into
    the magnetic interactions in the Mott insulator La2O2Fe2OSe2. This iron oxyselenide adopts a 2-k magnetic
    structure with low levels of magnetic frustration. This magnetic ground state is found to be dominated by
    next-nearest-neighbor interactions J2 and J2? and the magnetocrystalline anisotropy of the Fe2+ site, leading
    to 2D-Ising-like spin S = 2 fluctuations. In contrast to calculations, the values are small and confine the spin
    excitations below ?25 meV. This is further corroborated by sum rules of neutron scattering. This indicates that
    superconductivity in related materials may derive from a weakly coupled and unfrustrated magnetic structure.
  • McCabe, E., Stock, C., Bettis, J., Whangbo, M. and Evans, J. (2014). Magnetism of the Fe2+ and Ce3+ sublattices in Ce2 O2FeSe2: A combined neutron powder diffraction, inelastic neutron scattering, and density functional study. Physical Review B - Condensed Matter and Materials Physics [Online] 90:235115. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-84918552715&partnerID=40&md5=cdf22f69385b432aa365182d43319ffb.
    The discovery of superconductivity in the 122 iron selenide materials above 30 K necessitates an understanding of the underlying magnetic interactions. We present a combined experimental and theoretical investigation of magnetic and semiconducting Ce2O2FeSe2 composed of chains of edge-linked iron selenide tetrahedra. The combined neutron diffraction and inelastic scattering study and density functional calculations confirm the ferromagnetic nature of nearest-neighbor Fe-Se-Fe interactions in the ZrCuSiAs-related iron oxyselenide Ce2O2FeSe2. Inelastic measurements provide an estimate of the strength of nearest-neighbor Fe-Fe and Fe-Ce interactions. These are consistent with density functional theory calculations, which reveal that correlations in the Fe-Se sheets of Ce2O2FeSe2 are weak. The Fe on-site repulsion UFe is comparable to that reported for oxyarsenides and K1-xFe2-ySe2, which are parents to iron-based superconductors.
  • McCabe, E., Wills, A., Chapon, L., Manuel, P. and Evans, J. (2014). Structural and magnetic characterization of iron oxyselenides Ce2 O2 Fe2 OSe2 and Nd2 O2 Fe2 OSe2. Physical Review B - Condensed Matter and Materials Physics [Online] 90:165111. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-84908045015&partnerID=40&md5=8c308ae474e21a2d1c8f3d69afe1d070.
    We present here an investigation of the magnetic ordering in the Mott insulating oxyselenide materials Ln2O2Fe2OSe2 (Ln=Ce, Nd). Neutron powder diffraction data are consistent with a noncollinear multi-k ordering on the iron sublattice structure and analysis indicates a reduced magnetic correlation length perpendicular to the [Fe2O]2+ layers. The magnetic role of the Ln3+ cations is investigated and Ce3+ moments are found to order at Tâ?¤16 K.
  • Tuxworth, A., McCabe, E., Free, D., Clark, S. and Evans, J. (2013). Structural characterization and physical properties of the new transition metal oxyselenide La2O2ZnSe2. Inorganic Chemistry [Online] 52:2078-2085. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-84874023428&partnerID=40&md5=5f7f50a4aa835cd22bc5f32ccc51e38a.
    The quaternary transition metal oxyselenide La2O 2ZnSe2 has been shown to adopt a ZrCuSiAs-related structure with Zn2+ cations in a new ordered arrangement within the [ZnSe2]2- layers. This cation-ordered structure can be derived and described using the symmetry-adapted distortion mode approach. La2O2ZnSe2 is an direct gap semiconductor with an experimental optical band gap of 3.4(2) eV, consistent with electronic structure calculations. © 2013 American Chemical Society.
  • Giddings, A., Stennett, M., Reid, D., McCabe, E., Greaves, C. and Hyatt, N. (2011). Synthesis, structure and characterisation of the n=4 Aurivillius phase Bi5Ti3CrO15. Journal of Solid State Chemistry [Online] 184:252-263. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-79551681409&partnerID=40&md5=282f59d25c9631a31e620d547c79d420.
    The n=4 Aurivillius phase, Bi5Ti3CrO15, was synthesised by solid state reaction. Rietveld analysis of high resolution neutron diffraction data demonstrated this material to adopt the polar space group A21am at room temperature, transforming to the aristotype I4/mmm structure above 650 °C. This phase transition is coincident with an anomaly in DSC signal and relative permittivity, which are characteristic of a ferroelectricparaelectric phase transition. Bi5Ti3CrO 15 exhibits paramagnetic behaviour at low temperature, with short range antiferromagnetic interactions, but no evidence for long range magnetic ordering. This is considered a consequence of significant disorder of Ti and Cr over the available octahedral sites, as demonstrated by analysis of neutron diffraction data. © 2010 Elsevier Inc. All rights reserved.
  • McCabe, E., Free, D. and Evans, J. (2011). A new iron oxyselenide Ce2O2FeSe2: Synthesis and characterisation. Chemical Communications [Online] 47:1261-1263. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-78651330562&partnerID=40&md5=bef93c40d7a98a76848322c8430e7d97.
    In this communication we report the synthesis, structural and preliminary physical characterisation of a new layered oxyselenide Ce2O 2FeSe2. This material, containing a 1D portion of the structure of the layered FeSe-related superconductors, is a semiconductor with a band gap of around 0.64 eV and orders antiferromagnetically at low temperatures. © 2011 The Royal Society of Chemistry.
  • McCabe, E., Free, D., Mendis, B., Higgins, J. and Evans, J. (2010). Preparation, Characterization, and Structural Phase Transitions in a New Family of Semiconducting Transition Metal Oxychalcogenides ß-La2O2MSe2(M= Mn, Fe). Chemistry of Materials [Online] 22:6171-6182. Available at: http://dx.doi.org/10.1021/cm1023103.
    Two new oxyselenide materials have been synthesized with composition La2O2MSe2 (M = Mn, Fe). They adopt a new structure type, the ? structure, which has been solved and refined from powder X-ray and neutron diffraction data. The structure is described by Ama2 symmetry with unit cell 17.5 Å × 16.6 Å × 4.0 Å and consists of sheets of MSen polyhedra separated by La2O2Se blocks. A structural phase transition occurs on cooling involving ordering of M cations and a symmetry reduction to a primitive structure of Pna21 symmetry. Both manganese and iron analogues are antiferromagnetic at low temperature. ?-La2O2FeSe2 is a semiconductor in the temperature of 150?300 K with a band gap of approximately 0.7 eV while ?-La2O2MnSe2 is insulating at room temperature with band gap of 1.6 eV.
  • McCabe, E. and West, A. (2010). New high permittivity tetragonal tungsten bronze dielectrics Ba2LaMNb4O15: M=Mn, Fe. Journal of Solid State Chemistry [Online] 183:624-630. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-77649193098&partnerID=40&md5=72f440ee3b26021b1dcc3bde610a7966.
    The new phases Ba2LaMNb4O15: M=Mn, Fe were prepared by solid state reaction at 1100 °C. They have the tetragonal tungsten bronze structure, space group P4/mbm, at room temperature. The two octahedral sites show partial order of M and Nb with preferential occupancy of the smaller B(1) sites by M. Both phases have high permittivities 90±15 over the range 10-320 K. Ba2LaFeNb4O15 is highly insulating with bulk conductivity �10-8 ohm-1 cm-1 at 25 °C and tan δ�0.001 over the range 100-320 K and at 105 Hz. Solid solutions between these new phases and the compositionally and structurally related relaxor ferroelectric Ba2LaTi2Nb3O15 show gradual loss of ferroelectric behaviour attributed to replacement of polarisable Ti4+ by a mixture of (Mn, Fe)3+ and Nb5+. © 2010.
  • Liu, Y., McCabe, E., Sinclair, D. and West, A. (2009). Synthesis, structure and properties of the hexagonal perovskite, h-BaTi1-xHoxO3-x/2. Journal of Materials Chemistry [Online] 19:5201-5206. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-77949379472&partnerID=40&md5=85e1282302c20e9cf9b730a4662f54ca.
    The crystal structure of hexagonal (h)-BaTi0.85Ho 0.15O2.925 has been determined using neutron powder diffraction data. The structure is derived from that of h-BaTiO3 and contains Ho3+, the largest cation known to be accommodated by the B site in h-BaTiO3. Ti and Ho are disordered over the B1 octahedral sites and the structure may be regarded as intermediate between those of h-BaTiO3 and Ba3Sr(Nb,Ta)2O9. h-BaTi0.85Ho0.15O2.925 forms as a long-lived but metastable, intermediate phase before transforming, slowly, to the thermodynamically stable cubic polymorph of the same composition; its formation is an example of Ostwald's rule of successive reactions. It is an electrical insulator with relative permittivity of �50. © 2009 The Royal Society of Chemistry.
  • Rawal, R., McQueen, A., Gillie, L., Hyatt, N., McCabe, E., Samara, K., Alford, N., Feteira, A., Reaney, I. and Sinclair, D. (2009). Influence of octahedral tilting on the microwave dielectric properties of A3 LaNb3 O12 hexagonal perovskites (A=Ba, Sr). Applied Physics Letters [Online] 94:192904. Available at: https://doi.org/10.1063/1.3129867.
    Rietveld refinement of room temperature (RT) neutron diffraction (ND) data reveals 12R -type hexagonal perovskites Ba3 LaNb3 O 12 (BLN) and Sr3 LaNb3 O12 (SLN) to adopt space group R 3- with tilted NbO6 octahedra. The presence of an octahedral tilt transition (Ttilt) at 465 K in BLN from R 3- to R 3- m is proposed from a combination of high temperature ND data and fixed frequency permittivity measurements. Ttilt is estimated to be much higher at â?¼720 K for SLN. The large difference in the RT temperature coefficient of the resonant frequency (Ï?f), -100 ppm/K for BLN compared to -5 ppm/K for SLN, is attributed to the closer proximity of Ttilt to RT for BLN. Ï?f in these 12R -type hexagonal perovskites can therefore be tuned by controlling the tolerance factor and therefore Ttilt in a manner similar to that used for many Ba- and Sr-based 3C -type AB O3 perovskites. © 2009 American Institute of Physics.
  • Wu, Y., Pasero, D., McCabe, E., Matsushima, Y. and West, A. (2009). Partial cation-order and early-stage, phase separation in phase w, Li xCo1-xO: 0.075â?¤xâ?¤0.24-0.31. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences [Online] 465:1829-1841. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-67149107184&partnerID=40&md5=a0de639101d0c19b28eaa6d2c99abc60.
    We report the characterization using X-ray and neutron powder diffraction, transmission electron microscopy and extended X-ray absorption fine structure of a new, partially ordered rock-salt-like solid solution phase Li xCo1-xO: 0.075�x�0.24-0.31. The cation stacking sequence along [111] consists of alternating planes of Co and Co/Li. Nano-sized domains of this cation-ordered phase appear alongside disordered regions; domain size increases from 2 to 8 nm with increasing Li content. Compositions of ordered and disordered regions are Li- and Co-rich, respectively, and, therefore, the phase exhibits frozen-in, incipient phase separation. This microstructure could be considered as a precursor to precipitation of fully ordered, rhombohedral LiCoO2. © 2009 The Royal Society.
  • Wu, Y., Pasero, D., McCabe, E., Matsushima, Y. and West, A. (2009). Formation of disordered and partially ordered LixCo 1-xO. Journal of Materials Chemistry [Online] 19:1443-1448. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-61349187819&partnerID=40&md5=5f29cd527331b0c56d607ae509ed3eb5.
    Analysis of XRD, TG, XANES and density measurement data show that a new, partially-ordered, rock salt-like phase, W, exists for LixCo 1-xO, 0.075 â?¤ x â?¤ 0.24(2)-0.31(2), depending on temperature, with doping mechanism: 2Co2+ â?? Li+ + Co3+. Phase W forms as ordered domains within a cation-disordered rock salt solid solution based on CoO; domain size depends on temperature and composition. Binary phase diagrams of LixCo1-xO and phase W solid solutions in air and N2 are presented. © 2009 The Royal Society of Chemistry.
  • McCabe, E. and Greaves, C. (2008). Structural and magnetic characterisation of Aurivillius material Bi2Sr2Nb2.5Fe0.5O12. Journal of Solid State Chemistry [Online] 181:3051-3056. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-55549131889&partnerID=40&md5=3e454bf37fb2dffec3fdc4f566cbd09a.
    The n=3 Aurivillius material Bi2Sr2Nb2.5Fe0.5O12 is investigated and combined structural refinements using neutron powder diffraction (NPD) and X-ray powder diffraction data (XRPD) data reveal that the material adopts a disordered, tetragonal (I4/mmm) structure at temperatures down to 2 K. Significant ordering of Fe3+ and Nb5+ over the two B sites is observed and possible driving forces for this ordering are discussed. Some disorder of Sr2+ and Bi3+ over the M and A sites is found and is consistent with relieving strain due to size mismatch. Highly anisotropic thermal parameters for some oxygen sites suggest that the local structure may be slightly distorted with some rotation of the octahedra. Magnetic measurements show that the material behaves as a Curie-Weiss paramagnet in the temperature range studied with no evidence of any long-range magnetic interactions. Solid solutions including Bi3-xSrxNb2FeO12, Bi2Sr2-xLaxNb2FeO12 and Bi2Sr2Nb3-xFexO12 were investigated but single-phase materials were only successfully synthesised for a narrow composition range in the Bi2Sr2Nb3-xFexO12 system. © 2008 Elsevier Inc. All rights reserved.
  • McCabe, E. and Greaves, C. (2007). Fluorine insertion reactions into pre-formed metal oxides. Journal of Fluorine Chemistry [Online] 128:448-458. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-33947364859&partnerID=40&md5=a7d3e8c2122f01188388cead257fc250.
    Fluorine insertion reactions have been shown to be capable of modifying the physical properties of metal oxide materials, as a result of the structural and electronic consequences of fluorine insertion. This has been applied to copper oxide systems and has led to an enhanced understanding of the requirements for superconductivity, and more recently to other magnetic metal oxide systems where it has been shown to tune the magnetic properties of these materials. This review focuses on some important aspects of research on low temperature fluorine insertion reactions into pre-formed metal oxides, since 1998, and reports some new results. © 2006 Elsevier B.V. All rights reserved.
  • McCabe, E., Jones, I., Zhang, D., Hyatt, N. and Greaves, C. (2007). Crystal structure and electrical characterisation of Bi2NbO 5F: An Aurivillius oxide fluoride. Journal of Materials Chemistry [Online] 17:1193-1200. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-33947107022&partnerID=40&md5=a23d6f962b6c31f7b1abbc9ccc0b612a.
    Structural characterisation of Bi2NbO5F was performed using X-ray and neutron powder diffraction and electron diffraction. Structural refinements show that the material adopts a distorted structure with significant rotation of the octahedra around two axes. The physical properties of the material have been investigated and show no evidence of polar symmetry. The structure is therefore best described by space group Pbca (a = 5.428(1) �, b = 5.426(1) �, c = 16.656(1) �). Bond valence sum calculations suggest that ordering of the anions in the structure is favourable with the fluorine atoms preferring the apices of the NbX6 (X = O/F) octahedra. © The Royal Society of Chemistry 2007.
  • McCabe, E. and Greaves, C. (2006). Synthesis and structural and magnetic characterization of mixed manganese-copper n = 1 Ruddlesden-Popper phases. Chemistry of Materials [Online] 18:5774-5781. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-33845429129&partnerID=40&md5=215fb1a0a2bef7ead4cf54946baab3d1.
    New n = 1 Ruddlesden-Popper phases containing manganese and copper have been synthesized. Their structure has been investigated by X-ray and neutron powder diffraction and found to be tetragonal (14/mmm) at temperatures down to 10 K. The series of materials LaxSr2-xMn 0.5Cu0.5O4 (x = 0.75, 1, 1.25, 1.5) displays significant Jahn-Teller distortions of the B site cations, with the degree of distortion increasing with x. The materials LaSrMn0.5Cu 0.5O4, PrSrMn0.5Cu0.5O4, and NdSrMn0.5Cu0.5O4 show interesting magnetic behavior with antiferromagnetic ordering, but evidence of some ferromagnetic interactions. LaSrMn0.5Cu0.5O4 has long-range antiferromagnetic ordering and La0.5Sr0.5Mn 0.5Cu0.5O4 shows more complex behavior due to competing interactions, possibly resulting in a canted magnetic ground state. © 2006 American Chemical Society.
  • McCabe, E. and Greaves, C. (2005). Structural and magnetic characterisation of Bi2Sr 1.4La0.6Nb2MnO12 and its relationship to "Bi2Sr2Nb2MnO 12". Journal of Materials Chemistry [Online] 15:177-182. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-12444279055&partnerID=40&md5=4741ea10259ab9daaccf50c80be61e81.
    A new Aurivillius phase (generic formula M2An-IB nO3n+3) has been synthesized with n = 3 and containing manganese, Bi2Sr1.4La0.6Nb2MnO 12. The structure has been investigated by X-ray and neutron powder diffraction and found to be tetragonal (I4/mmm) at temperatures down to 2 K, with a= 3.89970(7) Ã?, c = 32.8073(9) Ã?at 2 K. There is significant cation disorder between Bi3+ (predominantly on the M sites) and Sr2+ and La3+ which prefer the A sites: 19(2)% of Bi 3+ occupy the A sites. This disorder, leading to occupancy of M sites by Sr2+, is thought to relieve strain due to size-mismatch between the fluorite-like and perovskite-like blocks. A high level of order exists between Mn and Nb on the B sites, with Mn located predominantly (76.1 (6)%) in the central B site whilst Nb preferentially occupies the lower symmetry, outer B site, where it undergoes an out-of-centre displacement towards the fluorite-like blocks. Magnetic measurements indicate that this material displays spin-glass behaviour on cooling. Synthesis of the Mn4+ analogue Bi2Sr2Nb2MnO12 was unsuccessful, possibly due to the small size of the Mn4+ cation.
  • Cheung, E., McCabe, E., Harris, K., Johnston, R., Tedesco, E., Raja, K. and Balaram, P. (2002). C - H ··· O hydrogen bond mediated chain reversal in a peptide containing a γ-amino acid residue, determined directly from powder X-ray diffraction data. Angewandte Chemie - International Edition [Online] 41:494-496. Available at: https://doi.org/10.1002/1521-3773(20020201)41:3<494::AID-ANIE494>3.0.CO;2-S.
    Similar to the classical β turn: An intramolecular cyclic 10-atom motif is defined in the molecular conformation of Piv-LPRO-γ-Abu-NHMe (see powder X-ray diffraction structure; Piv: pivaloyl, Lpro: L-proline, γ-Abu: γ-aminobutyric acid) by a C - H ··· O interaction. This study emphasizes the considerable potential of powder X-ray diffraction as an alternative to single-crystal X-ray diffraction.
Last updated