Portrait of Professor Alan Chadwick

Professor Alan Chadwick

Emeritus Professor of Physical Chemistry

About

I was born in Manchester to a family that had supported Newton Heath Loco from the time of its inception. I went to Gorton Mount Primary School and passed the 11 plus to go to Burnage Grammar School for Boys. I then studied chemistry at Manchester University for both BSc and PhD degrees. I finished the PhD in 1966, the year England won the World Cup, the height of Beatles mania and Swinging London. I missed the latter as I was in Ottawa, Canada at the National Research Council of Canada as a post-doctoral fellow. However, I did see Expo in Montreal and saw Charles de Gaulle at the now infamous ‘Quebec Libre’ visit. I was also given the chance to see a lot of Canada and the northern USA. After Canada I had another two year as a post-doctoral fellow at Strathclyde University in Glasgow. This was a dramatic change and I really enjoyed Glasgow, the place the people and the research. In 1970 I came to Kent as a lecturer in chemistry for what I expected to be a ‘few years’. The fact that I am still here is evidence for my lasting respect and affection for place and the people.

Research interests

My research career has centred on solid state chemistry, beginning when this was a very niche area of chemistry through to the current popularity of materials chemistry. I have worked on a very wide range of topics, namely defects and diffusion solids, including ionic, molecular and polymeric materials, electrical transport in polar solids, solid electrolytes, (superionic or fast-ion conductors) and nanocrystalline materials. The techniques I have employed have been very wide and have included structural methods, including X-ray absorption fine-structure (XAS) spectroscopy and NMR, computer modelling of solids and chemical sensor development. My current research is now centred on two areas; energy materials and archaeology. In 2004 I was a founder member of the on-going Alistore EU project to improve lithium-ion batteries. I led the platform using synchrotron radiation in characterising materials. This has now widened to energy materials (materials for batteries, fuel cells, photovoltaics, etc.) and I coordinate a consortium at the Diamond Light Source studying these systems. Also in 2004 I began collaboration with the Mary Rose Trust with the aim of using XAS to study the conservation problems in the ship. This research continues with a focus on the ‘sulfur problem’, the attack on the timbers by sulfuric acid formed by the oxidation of sulfur compounds in the wood.

Publications

Showing 50 of 142 total publications in the Kent Academic Repository. View all publications.

Article

  • Yang, C., Rousse, G., Louise Svane, K., Pearce, P., Abakumov, A., Deschamps, M., Cibin, G., Chadwick, A., Dalla Corte, D., Anton Hansen, H., Vegge, T., Tarascon, J. and Grimaud, A. (2020). Cation insertion to break the activity/stability relationship for highly active oxygen evolution reaction catalyst. Nature Communications [Online] 11. Available at: https://doi.org/10.1038/s41467-020-15231-x.
    The production of hydrogen at a large scale by the environmentally-friendly electrolysis process is currently hampered by the slow kinetics of the oxygen evolution reaction (OER). We report a solid electrocatalyst α-Li2IrO3 which upon oxidation/delithiation chemically reacts with water to form a hydrated birnessite phase, the OER activity of which is five times greater than its non-reacted counterpart. This reaction enlists a bulk redox process during which hydrated potassium ions from the alkaline electrolyte are inserted into the structure while water is oxidized and oxygen evolved. This singular charge balance process for which the electrocatalyst is solid but the reaction is homogeneous in nature allows stabilizing the surface of the catalyst while ensuring stable OER performances, thus breaking the activity/stability tradeoff normally encountered for OER catalysts.
  • Kim, E., Ma, L., Duda, L., Pickup, D., Chadwick, A., Younesi, R., Irvine, J. and Armstrong, A. (2020). Oxygen Redox Activity through a Reductive Coupling Mechanism in the P3-Type Nickel-Doped Sodium Manganese Oxide. ACS Applied Energy Materials [Online] 3:184-191. Available at: https://doi.org/10.1021/acsaem.9b02171.
    Increasing dependence on rechargeable batteries for energy storage calls for the improvement of energy density of batteries. Toward this goal, introduction of positive electrode materials with high voltage and/or high capacity is in high demand. The use of oxygen chemistry in lithium and sodium layered oxides has been of interest to achieve high capacity. Nevertheless, a complete understanding of oxygen-based redox processes remains elusive especially in sodium ion batteries. Herein, a novel P3-type \(Na_{0.67}Ni_{0.2}Mn_{0.8}O_2\), synthesized at low temperature, exhibits oxygen redox activity in high potentials. Characterization using a range of spectroscopic techniques reveals the anionic redox activity is stabilized by the reduction of Ni, because of the strong Ni 3d–O 2p hybridization states created during charge. This observation suggests that different route of oxygen redox processes occur in P3 structure materials, which can lead to the exploration of oxygen redox chemistry for further development in rechargeable batteries.
  • McLeod, L., Spikes, G., Kashtiban, R., Walker, M., Chadwick, A., Sharman, J. and Walton, R. (2020). Structures of mixed manganese ruthenium oxides \ (Mn_{1−x}Ru_x)O_2\) crystallised under acidic hydrothermal conditions. Dalton Transactions [Online] 49:2661-2670. Available at: https://doi.org/10.1039/C9DT04156G.
    A synthesis method for the preparation of mixed manganese–ruthenium oxides is presented along with a detailed characterisation of the solids produced. The use of 1 M aqueous sulfuric acid mediates the redox reaction between KRuO\(_4\), KMnO\(_4\) and Mn\(^{2+}\) to form ternary oxides. At reaction temperature of 100°C the products are mixtures of α-MnO\(_2\) (hollandite-type) and β-MnO\(_2\) (rutile-type), with some evidence of Ru incorporation in each from their expanded unit cell volumes. At reaction temperature of 200°C solid-solutions β-Mn\(_{1−x}\)Ru\(_x\)O\(_2\) are formed and materials with x ≤ 0.6 have been studied. The amount of Ru included in the oxide is greater than expected from the ratio of metals used in the synthesis, as determined by elemental analysis, implying that some Mn remains unreacted in solution. Powder X-ray diffraction (XRD) shows that while the unit cell volume expands in a linear manner, following Vegard's law, the tetragonal lattice parameters, and the a/c ratio, do not follow the extrapolated trends: this anisotropic behaviour is consistent with the different local coordination of the metals in the end members. Powder XRD patterns show increased peak broadening with increasing ruthenium content, which is corroborated by electron microscopy that shows nanocrystalline material. X-ray absorption near-edge spectra show that the average oxidation state of Mn in the solid solutions is reduced below +4 while that of Ru is increased above +4, suggesting some redistribution of charge. Analysis of the extended X-ray absorption fine structure provides complementary local structural information, confirming the formation of a solid solution, while X-ray photoelectron spectroscopy shows that the surface oxidation states of both Ru and Mn are on average lower than +4, suggesting a disordered surface layer may be present in the materials.
  • House, R., Maitra, U., Jin, L., Lozano, J., Somerville, J., Rees, N., Naylor, A., Duda, L., Massel, F., Chadwick, A., Ramos, S., Pickup, D., McNally, D., Lu, X., Schmitt, T., Roberts, M. and Bruce, P. (2019). What Triggers Oxygen Loss in Oxygen Redox Cathode Materials?. Chemistry of Materials [Online] 31:3293-3300. Available at: https://doi.org/10.1021/acs.chemmater.9b00227.
    It is possible to increase the charge capacity of transition-metal (TM) oxide cathodes in alkali-ion batteries by invoking redox reactions on the oxygen. However, oxygen loss often occurs. To explore what affects oxygen loss in oxygen redox materials, we have compared two analogous Na-ion cathodes, P2-Na0.67Mg0.28Mn0.72O2 and P2-Na0.78Li0.25Mn0.75O2. On charging to 4.5 V, >0.4e– are removed from the oxide ions of these materials, but neither compound exhibits oxygen loss. Li is retained in P2-Na0.78Li0.25Mn0.75O2 but displaced from the TM to the alkali metal layers, showing that vacancies in the TM layers, which also occur in other oxygen redox compounds that exhibit oxygen loss such as Li[Li0.2Ni0.2Mn0.6]O2, are not a trigger for oxygen loss. On charging at 5 V, P2-Na0.78Li0.25Mn0.75O2 exhibits oxygen loss, whereas P2-Na0.67Mg0.28Mn0.72O2 does not. Under these conditions, both Na+ and Li+ are removed from P2-Na0.78Li0.25Mn0.75O2, resulting in underbonded oxygen (fewer than 3 cations coordinating oxygen) and surface-localized O loss. In contrast, for P2-Na0.67Mg0.28Mn0.72O2, oxygen remains coordinated by at least 2 Mn4+ and 1 Mg2+ ions, stabilizing the oxygen and avoiding oxygen loss.
  • Düvel, A., Morgan, L., Cibin, G., Pickup, D., Chadwick, A., Heitjans, P. and Sayle, D. (2018). Tuning Anti-Site Defect Density in Perovskite-BaLiF3 via Ball-Milling/Heating-Cycling. The Journal of Physical Chemistry Letters [Online] 9:5121-5124. Available at: https://doi.org/10.1021/acs.jpclett.8b01915.
    The defect density of a material is central to its prop-erties. Here, we show, employing EXAFS measure-ments and MD simulation, how the Ba-Li anti-site defect density of perovskite-structured BaLiF3 nano-particles can be tuned. In particular, we show that ball milling reduces the defect content. Conversely, thermal annealing increases the defect density. The work represents a first step towards tailoring the properties of a material, via defect tuning post syn-thesis.
  • Cook, D., Clarkson, G., Dawson, D., Ashbrook, S., Fisher, J., Thompsett, D., Pickup, D., Chadwick, A. and Walton, R. (2018). Alkaline-Earth Rhodium Hydroxides: Synthesis, Structures, and Thermal Decomposition to Complex Oxides. Inorganic Chemistry [Online] 57:11217-11224. Available at: https://doi.org/10.1021/acs.inorgchem.8b01797?.
    The rhodium (III) hydrogarnets Ca3Rh2(OH)12 and Sr3Rh2(OH)12 crystallise as polycrystalline powders under hydrothermal conditions at 200°C from RhCl3·3H2O and either Ca(OH)2 or Sr(OH)2 in either 12 M NaOH or KOH. Rietveld refinements against synchrotron powder X-ray diffraction (XRD) data allow the first crystal structures of the two materials to be determined. If BaO2 is used as a reagent and the concentration of hydroxide increased to hydroflux conditions (excess NaOH) then single crystals of a new complex rhodium hydroxide, BaNaRh(OH)6, are formed in a phase-pure sample, with sodium included from the flux. Structure solution from single-crystal XRD data reveals isolated octahedral Rh centres that share hydroxides with 10-coordinate Ba and two independent 8-coordinate Na sites. 23Na magic-angle spinning NMR confirms the presence of the two crystallographically distinct Na sites and also verifies the diamagnetic nature of the sample, expected for Rh(III). The thermal behaviour of the hydroxides on heating in air was investigated using X-ray thermodiffractometry, showing different decomposition pathways for each material. Ca3Rh2(OH)12 yields CaRh2O4 and CaO above 650°C, from which phase-pure CaRh2O4 is isolated by washing with dilute nitric acid, a material previously only reported by high-pressure or high-temperature synthesis. Sr3Rh2(OH)12 decomposes to give a less crystalline material with a powder XRD pattern that is matched to the 2H-layered hexagonal perovskite Sr6Rh5O15, which contains mixed-valent Rh3+/4+, confirmed by Rh K-edge XANES spectroscopy. On heating BaNaRh(OH)6 a complex set of decomposition events takes place via transient phases.
  • Somerville, J., Tapia-Ruiz, N., Sobkowiak, A., House, R., Ramos, S., Chadwick, A., Roberts, M., Maitra, U. and Bruce, P. (2018). Identification and Characterisation of High Energy Density P2-Type Na2/3[Ni1/3-y/2Mn2/3-y/2Fey]O2 Compounds for Na-ion Batteries. Journal of Materials Chemistry A [Online] 6:5231-5462. Available at: http://dx.doi.org/10.1039/C7TA09607K.
    The composition space between MnO2, NaFeO2, and Na[Ni1/2Mn1/2]O2 has been explored with the goal of identifying Earth-abundant single-phase P2 cathode materials. This has led to the identification of two compounds, P2 Na2/3[Ni1/3-y/2Mn2/3-y/2Fey]O2 (y = 1/6, 1/3) which exhibit state of the art specific energies. These materials were further evaluated through galvanostatic cycling and x-ray absorption spectroscopy.
  • Somerville, J., House, R., Tapia-Ruiz, N., Sobkowiak, A., Ramos, S., Chadwick, A., Roberts, M., Maitra, U. and Bruce, P. (2018). Identification and characterisation of high energy density P2-type Na2/3[Ni1/3−y/2Mn2/3−y/2Fey]O2 compounds for Na-ion batteries. Journal of Materials Chemistry A [Online] 6:5271-5275. Available at: https://doi.org/10.1039/C7TA09607K.
    The composition space between MnO2, NaFeO2, and Na[Ni1/2Mn1/2]O2 has been explored with the goal of identifying Earth-abundant single-phase P2 cathode materials. This has led to the identification of two compounds, P2-Na2/3[Ni1/3−y/2Mn2/3−y/2Fey]O2 (y = 1/6, 1/3) which exhibit state of the art specific energies. These materials were further evaluated through galvanostatic cycling and X-ray absorption spectroscopy.
  • Maitra, U., House, R., Somerville, J., Tapia-Ruiz, N., Lozano, J., Guerrini, N., Hao, R., Luo, K., Jin, L., Pérez-Osorio, M., Massel, F., Pickup, D., Ramos, S., Lu, X., McNally, D., Chadwick, A., Giustino, F., Schmitt, T., Duda, L., Roberts, M. and Bruce, P. (2018). Oxygen redox chemistry without excess alkali-metal ions in Na\(_{2/3}\)[Mg\(_{0.28}\)Mn\(_{0.72}\)]O\(_2\). Nature Chemistry [Online] 10:288-295. Available at: https://dx.doi.org/10.1038/nchem.2923.
    The search for improved energy-storage materials has revealed Li- and Na-rich intercalation compounds as promising high-capacity cathodes. They exhibit capacities in excess of what would be expected from alkali-ion removal/reinsertion and charge compensation by transition-metal (TM) ions. The additional capacity is provided through charge compensation by oxygen redox chemistry and some oxygen loss. It has been reported previously that oxygen redox occurs in O 2\(p\) orbitals that interact with alkali ions in the TM and alkali-ion layers (that is, oxygen redox occurs in compounds containing Li\(^+\)–O(2\(p\))–Li\(^+\) interactions). Na\(_{2/3}\)[Mg\(_{0.28}\)Mn\(_{0.72}\)]O\(_2\) exhibits an excess capacity and here we show that this is caused by oxygen redox, even though Mg\(^{2+}\) resides in the TM layers rather than alkali-metal (AM) ions, which demonstrates that excess AM ions are not required to activate oxygen redox. We also show that, unlike the alkali-rich compounds, Na\(_{2/3}\)[Mg\(_{0.28}\)Mn\(_{0.72}\)]O\(_2\) does not lose oxygen. The extraction of alkali ions from the alkali and TM layers in the alkali-rich compounds results in severely underbonded oxygen, which promotes oxygen loss, whereas Mg\(^{2+}\) remains in Na\(_{2/3}\)[Mg\(_{0.28}\)Mn\(_{0.72}\)]O\(_2\), which stabilizes oxygen.
  • Fehse, M., Darwiche, A., Sougrati, M., Kelder, E., Chadwick, A., Alfredsson, M., Monconduit, L. and Stievano, L. (2017). In-Depth Analysis of the Conversion Mechanism of TiSnSb vs Li by Operando Triple-Edge X-ray Absorption Spectroscopy: a Chemometric Approach. Chemistry of Materials [Online] 29:10446-10454. Available at: https://doi.org/10.1021/acs.chemmater.7b04088.
    The electrochemical cycling mechanism of the ternary intermetallic TiSnSb, a promising conversion-type negative electrode material for lithium batteries, was thoroughly studied by operando X-ray absorption spectroscopy (XAS) at three different absorption edges, i.e., Ti, Sn, and Sb K-edge. Chemometric tools such as principal component analysis and multivariate curve resolution-alternating least squares were applied on the extensive data set to extract the maximum contained information in the whole set of operando data. The evolution of the near-edge (XANES) fingerprint and of the extended fine-structure (EXAFS) of the XAS spectra confirms the reversibility of the conversion mechanism, revealing that Ti forms metallic nanoparticles upon lithiation and binds back to both Sn and Sb upon the following delithiation. The formation of both Li7Sn2 and Li3Sb upon lithiation was also clearly confirmed. The application of chemometric tools allowed the identification of a time shift between the reaction processes of Sn and Sb lithiation, indicating that the two metals do not react at the same time, in spite of a certain overlap between their respective reaction. Furthermore, XANES and EXAFS fingerprint show that the Ti–Sn–Sb species formed after one complete lithiation/delithiation cycle is distinct from the starting material TiSnSb.
  • Yang, C., Laberty-Robert, C., Batuk, D., Cibin, G., Chadwick, A., Pimenta, V., Yin, W., Zhang, L., Tarascon, J. and Grimaud, A. (2017). Phosphate Ion Functionalization of Perovskite Surfaces for Enhanced Oxygen Evolution Reaction. The Journal of Physical Chemistry Letters [Online] 8:3466-3472. Available at: http://dx.doi.org/10.1021/acs.jpclett.7b01504.
    Recent findings revealed that surface oxygen can participate in the oxygen evolution reaction (OER) for the most active catalysts, which eventually triggers a new mechanism for which the deprotonation of surface intermediates limits the OER activity. We propose in this work a “dual strategy” in which tuning the electronic properties of the oxide, such as La1–xSrxCoO3??, can be dissociated from the use of surface functionalization with phosphate ion groups (Pi) that enhances the interfacial proton transfer. Results show that the Pi functionalized La0.5Sr0.5CoO3?? gives rise to a significant enhancement of the OER activity when compared to La0.5Sr0.5CoO3?? and LaCoO3. We further demonstrate that the Pi surface functionalization selectivity enhances the activity when the OER kinetics is limited by the proton transfer. Finally, this work suggests that tuning the catalytic activity by such a “dual approach” may be a new and largely unexplored avenue for the design of novel high-performance catalysts.
  • Prutsch, D., Breuer, S., Uitz, M., Bottke, P., Langer, J., Lunghammer, S., Philipp, M., Posch, P., Pregartner, V., Stanje, B., Dunst, A., Wohlmuth, D., Brandstätter, H., Schmidt, W., Epp, V., Chadwick, A., Hanzu, I. and Wilkening, M. (2017). Nanostructured Ceramics: Ionic Transport and Electrochemical Activity. Zeitschrift für Physikalische Chemie [Online] 231. Available at: https://doi.org/10.1515/zpch-2016-0924.
    Ceramics with nm-sized dimensions are widely used in various applications such as batteries, fuel cells or sensors. Their oftentimes superior electrochemical properties as well as their capabilities to easily conduct ions are, however, not completely understood. Depending on the method chosen to prepare the materials, nanostructured ceramics may be equipped with a large area fraction of interfacial regions that exhibit structural disorder. Elucidating the relationship between microscopic disorder and ion dynamics as well as electrochemical performance is necessary to develop new functionalized materials. Here, we highlight some of the very recent studies on ion transport and electrochemical properties of nanostructured ceramics. Emphasis is put on TiO2 in the form of nanorods, nanotubes or being present as mesoporous material. Further examples deal with nanocrystalline peroxides such as Li2O2 or nanostructured oxides (Li2TiO3, LiAlO2, LiTaO3, Li2CO3 and Li2B4O7). These materials served as model systems to explore the influence of ball-milling on overall ionic transport.
  • Düvel, A., Heitjans, P., Fedorov, P., Scholz, G., Cibin, G., Chadwick, A., Pickup, D., Ramos, S., Sayle, L., Sayle, E., Sayle, T. and Sayle, D. (2017). Is Geometric Frustration-Induced Disorder a Recipe for High Ionic Conductivity?. Journal of the American Chemical Society [Online] 139:5842-5848. Available at: https://doi.org/10.1021/jacs.7b00502.
    Ionic conductivity is ubiquitous to many industrially important applications such as fuel cells, batteries, sensors, and catalysis. Tunable conductivity in these systems is therefore key to their commercial viability. Here, we show that geometric frustration can be exploited as a vehicle for conductivity tuning. In particular, we imposed geometric frustration upon a prototypical system, CaF2, by ball milling it with BaF2, to create nanostructured Ba1–xCaxF2 solid solutions and increased its ionic conductivity by over 5 orders of magnitude. By mirroring each experiment with MD simulation, including “simulating synthesis”, we reveal that geometric frustration confers, on a system at ambient temperature, structural and dynamical attributes that are typically associated with heating a material above its superionic transition temperature. These include structural disorder, excess volume, pseudovacancy arrays, and collective transport mechanisms; we show that the excess volume correlates with ionic conductivity for the Ba1–xCaxF2 system. We also present evidence that geometric frustration-induced conductivity is a general phenomenon, which may help explain the high ionic conductivity in doped fluorite-structured oxides such as ceria and zirconia, with application for solid oxide fuel cells. A review on geometric frustration [ Nature 2015, 521, 303] remarks that classical crystallography is inadequate to describe systems with correlated disorder, but that correlated disorder has clear crystallographic signatures. Here, we identify two possible crystallographic signatures of geometric frustration: excess volume and correlated “snake-like” ionic transport; the latter infers correlated disorder. In particular, as one ion in the chain moves, all the other (correlated) ions in the chain move simultaneously. Critically, our simulations reveal snake-like chains, over 40 Å in length, which indicates long-range correlation in our disordered systems. Similarly, collective transport in glassy materials is well documented [for example, J. Chem. Phys. 2013, 138, 12A538]. Possible crystallographic nomenclatures, to be used to describe long-range order in disordered systems, may include, for example, the shape, length, and branching of the “snake” arrays. Such characterizations may ultimately provide insight and differences between long-range order in disordered, amorphous, or liquid states and processes such as ionic conductivity, melting, and crystallization.
  • Chadwick, A., Pickup, D., Ramos, S., Cibin, G., Tapia-Ruiz, N., Breuer, S., Wohlmuth, D. and Wilkening, M. (2017). An X-Ray Absorption Spectroscopy Study of Ball-Milled Lithium Tantalate and Lithium Titanate Nanocrystals. IOP Conference Series: Materials Science and Engineering [Online] 169. Available at: https://doi.org/10.1088/1757-899X/169/1/012015.
    Previous work has shown that nanocrystalline samples of lithium tantalate and titanate prepared by high-energy milling show unusually high lithium ion conductivity. Here, we report an X-ray absorption spectroscopy (XAS) study at the Ti K-edge and the Ta L3 edge of samples that have been milled for various lengths of time. For both systems the results show that milling creates amorphous material whose quantity increases with the milling time. The more extensive data for the tantalate shows that milling for only 30 minutes generates ~25% amorphous content in the sample. The content rises to ~60% after 16 hours. It is suggested that it is the motion of the lithium ions through the amorphous content that provides the mechanism for the high ionic conductivity.
  • Kiss, B., Manning, T., Hesp, D., Didier, C., Taylor, A., Pickup, D., Chadwick, A., Allison, H., Dhanak, V., Claridge, J., Darwent, J. and Rosseinsky, M. (2017). Nano-structured rhodium doped SrTiO3–Visible light activated photocatalyst for water decontamination. Applied Catalysis B: Environmental [Online] 206:547-555. Available at: https://doi.org/10.1016/j.apcatb.2017.01.066.
    A modified hydrothermal synthesis, avoiding high temperature calcination, is used to produce nano-particulate rhodium doped strontium titanate in a single-step, maintaining the rhodium in the photocatalytically active +3 oxidation state as shown by X-ray spectroscopy. The photoactivity of the material is demonstrated through the decomposition of aqueous methyl orange and the killing of Escherichia coli in aqueous suspension, both under visible light activation. A sample of SrTiO3 containing 5 at% Rh completely decomposed a solution of methyl orange in less than 40 min and E. coli is deactivated within 6 h under visible light irradiation.
  • Chadwick, A., Berko, A., Schofield, E., Smith, A., Mosselmans, J., Jones, A. and Cibin, G. (2016). The application of X-ray absorption spectroscopy in archaeological conservation: Example of an artefact from Henry VIII warship, the Mary Rose. Journal of Non-Crystalline Solids [Online] 451:49-55. Available at: http://doi.org/10.1016/j.jnoncrysol.2016.05.020.
    We report a microfocus X-ray absorption (XAS) investigation of a thin film sample from an iron contaminated wooden arrow tip raised from the seabed with the Mary Rose. The XAS studies were combined with optical and scanning electron microscopy measurements. The arrow tip had been treated with polyethylene glycol (PEG) soon after it had been raised and stored in a controlled environment. The measurements revealed a significant concentration of iron sulfide nanoparticles. This indicates that in this sample there was a reduction of the oxidative effects of the normal ambient atmosphere that is usually seen in untreated timbers. The film was treated overnight with an aqueous solution of diethylenetriaminepentaacetic acid (DTPA), which is normally very effective in sequestering iron. This had little effect in terms of removing iron from the film and possible explanations are discussed.
  • Luo, K., Roberts, M., Hao, R., Guerrini, N., Pickup, D., Liu, Y., Edström, K., Guo, J., Chadwick, A., Duda, L. and Bruce, P. (2016). Charge-compensation in 3d-transition-metal-oxide intercalation cathodes through the generation of localized electron holes on oxygen. Nature Chemistry [Online]:684-691. Available at: http://dx.doi.org/10.1038/nchem.2471.
  • Poll, C., Nelson, G., Pickup, D., Chadwick, A., Riley, D. and Payne, D. (2016). Electrochemical recycling of lead from hybrid organic–inorganic perovskites using deep eutectic solvents. Green Chemistry [Online] 18:2946-2955. Available at: http://dx.doi.org/10.1039/C5GC02734A.
    The emerging field of lead-based hybrid organic–inorganic perovskite (HOIP) photovoltaic devices has attracted a great deal of attention due to their very high conversion efficiencies and straightforward fabrication methods. Unfortunately, a major obstacle to commercialization remains the high toxicity of lead. Whilst to date the focus has been on understanding and improving device performance, there has been no reported effort to develop methods to recover and recycle the lead from these materials. In this work we demonstrate a simple, low-cost and environmentally friendly method of recycling lead from HOIP photovoltaics by dissolution and selective electrodeposition using a deep eutectic solvent. We demonstrate that up to 99.8% of the lead is removed from the solvent. The results presented here provide a viable solution to lead-based HOIP photovoltaic recycling, and also open the possibility for providing an alternative method to conventional smelting in the recovery and recycling of different lead-based energy materials.
  • Rammutla, K., Comins, J., Erasmus, R., Netshisaulu, T., Ngoepe, P. and Chadwick, A. (2015). Light scattering and computer simulation studies of superionic pure and La-doped BaF2. Chemical Physics [Online] 467:6-12. Available at: http://dx.doi.org/10.1016/j.chemphys.2015.12.004.
    A combination of both Raman and Brillouin scattering experiments as well as Molecular Dynamics (MD) was used to study the superionic behaviour of BaF2 doped with a wide range of LaF3 concentrations (0 ? x ? 50 mol%). Raman spectroscopy reveals that for undoped BaF2 and those doped with 5% and 10% LaF3, the room temperature spectra show the usual T2g symmetry mode at 241 cm?1 whereas for those doped with 20%, 30% and 50% LaF3, the dominant Raman mode is of the Eg symmetry situated at ?263, 275 and 286 cm?1, respectively. The Raman linewidths show near linear increases with temperature followed by rapid increases above the characteristic transition temperatures (Tc), being at 1200, 850, 800, 975, 950 and 920 K for LaF3 concentrations of 0, 5, 10, 20, 30 and 50; respectively. The temperature dependence of the squares of the Brillouin frequencies (??B)2 of the LA and TA acoustic modes respectively related to elastic constants C11 and C44 showed linear decreases followed by significant deviations around the same temperatures (Tc), at which the Raman linewidths start to show substantial increases. The complementary studies using MD simulations show that the diffusion coefficients increase markedly above the same temperatures observed experimentally. The extrinsic fluorine ion trajectories were also determined from the MD simulations to better understand the mechanisms of diffusion.
  • Schofield, E., Sarangi, R., Mehta, A., Jones, A., Smith, A., Mosselmans, J. and Chadwick, A. (2015). Strontium carbonate nanoparticles for the surface treatment of problematic sulfur and iron in waterlogged archaeological wood. Journal of Cultural Heritage [Online] 18:306-312. Available at: http://dx.doi.org/10.1016/j.culher.2015.07.013.
    Stabilising waterlogged archaeological wooden artefacts for display presents a challenge for conservators and scientists. Sulfur compounds, incorporated into the wood prior to excavation, can lead to acid formation when exposed to oxygen, and in the presence of iron ions. Strontium carbonate nanoparticles have recently been shown to reduce the production of acid formation at the root by reacting with inorganic sulfur-containing compounds. Here, we show the feasibility of using this treatment on small samples where consolidating treatments have already been performed. It is found that PEG 200 does not prevent the reactivity of the nanoparticles with the sulfur compounds present in the artefacts. A surface brushing application method was found to be successful whilst retaining the visual integrity. In addition, it was found that this technique results in the leaching of iron from the surface layers, preventing future build up of acid catalysed by iron compounds.
  • Chadwick, A., Düvel, A., Heitjans, P., Pickup, D., Ramos, S., Sayle, D. and Sayle, T. (2015). X-Ray Absorption Spectroscopy and Computer Modelling Study of Nanocrystalline Binary Alkaline Earth Fluorides. IOP Conference Series: Materials Science and Engineering [Online] 80:12005. Available at: http://doi.org/10.1088/1757-899X/80/1/012005.
    Nanocrystalline samples of Ba1-xCaxF2 prepared by high-energy milling show an unusually high F? ion conductivity, which exhibit a maximum in the magnitude and a minimum in the activation energy at x = 0.5. Here, we report an X-ray absorption spectroscopy (XAS) at the Ca and Sr K edges and the Ba L3 edge and a molecular dynamics (MD) simulation study of the pure and mixed fluorides. The XAS measurements on the pure binary fluorides, CaF2, SrF2 and BaF2 show that high-energy ball-milling produces very little amorphous material, in contrast to the results for ball milled oxides. XAS measurements of Ba1-xCaxF2 reveal that for 0 < x <1 there is considerable disorder in the local environments of the cations which is highest for x = 0.5. Hence the maximum in the conductivity corresponds to the composition with the maximum level of local disorder. The MD calculations also show a highly disordered structure consistent with the XAS results and similarly showing maximum disorder at x = 0.5.
  • Brownrigg, A., Mountjoy, G., Chadwick, A., Alfredsson, M., Bras, W., Billaud, J., Armstrong, A., Bruce, P., Dominko, R. and Kelder, E. (2015). In situ Fe K-edge X-ray absorption spectroscopy study during cycling of Li\(_2\)FeSiO\(_4\) and Li\(_{2.2}\)Fe\(_{0.9}\)SiO\(_4\) Li ion battery materials. Journal of Materials Chemistry A [Online] 3:7314-7322. Available at: http://www.dx.doi.org/10.1039/c4ta06305h.
    In situ X-ray Absorption Spectroscopy (XAS) results are presented for Li\(_2\)FeSiO\(_4\) and Li\(_{2.2}\)Fe\(_{0.9}\)SiO\(_4\), promising cathode materials for lithium-ion batteries. The aims are to establish the valence and local structure of Fe during charge and discharge to understand if the Fe\(^{3+}\)/Fe\(^{4+}\) redox pair can be reached in the current battery design. It is found that the valence state changes between Fe\(^{2+}\) and Fe\(^{3+}\), with no evidence of Fe\(^{4+}\) before the onset of electrolyte degradation. There is a reversible contraction and extension of the Fe–O bond lengths during cycling while the Fe–Si distance remains constant, which underlines the stability of the Li\(_2\)FeSiO\(_4\) material. The same observations apply to Li\(_{2.2}\)Fe\(_{0.9}\)SiO4 cathode material indicating that changing the stoichiometry does not provide any additional structural stability.
  • Chadwick, A., Howland, K., Went, M., Schofield, E. and Jones, A. (2014). The Application of Ionic Nanoparticles in the Conservation of Archaelogical Wood. Macromolecular Symposia [Online] 337:74-79. Available at: http://dx.doi.org/10.1002/masy.201450308.
    Summary: A potential method for the de-acidification of water-logged archaeological
    wood is through a treatment with alkaline nanoparticles. In previous studies,
    we have shown that strontium carbonate nanoparticles are especially effective in
    removing sulfuric acid from the Mary Rose timbers. In this contribution, we report
    the effect of these nanoparticles on other known sulfur compounds in the timbers.
    Overall, these effects are beneficial, yielding benign compounds and removing the
    possibility for the conversion to sulfuric acid.
  • Moulki, H., Faure, C., Mihelcic, M., Surca Vuk, A., Svegl, F., Orel, B., Campet, G., Alfredsson, M., Chadwick, A., Gianolio, D. and Rougier, A. (2014). Electrochromic performances of nonstoichiometric NiO thin films. Thin Solid Films [Online] 553:63-66. Available at: http://www.dx.doi.org/10.1016/j.tsf.2013.10.154.
    Electrochromic (EC) performances of Ni3 + containing NiO thin films, called modified NiO thin films, prepared either by pulsed laser deposition or by chemical route are reported. When cycled in lithium based electrolyte, the comparison of the EC behavior of nonstoichiometric NiO thin films points out a larger optical contrast for the films synthesized by chemical route with the absence of an activation period on early electrochemical cycling due in particular to a larger porosity. Herein we demonstrate faster kinetics for modified NiO thin films cycled in lithium ion free electrolyte. Finally, X-ray absorption spectroscopy is used for a preliminary understanding of the mechanism involved in this original EC behavior linked to the film characteristics including their disorder character, the presence of Ni3 + and their porous morphology.
  • Preston, J., Smith, A., Schofield, E., Chadwick, A., Jones, M. and Watts, J. (2014). The Effects of Mary Rose Conservation Treatment on Iron Oxidation Processes and Microbial Communities Contributing to Acid Production in Marine Archaeological Timbers. PLoS ONE [Online] 9:e84169. Available at: http://dx.doi.org/10.1371/journal.pone.0084169.
    The Tudor warship the Mary Rose has reached an important transition point in her conservation. The 19 year long process of spraying with polyethylene glycol (PEG) has been completed (April 29th 2013) and the hull is air drying under tightly controlled conditions. Acidophilic bacteria capable of oxidising iron and sulfur have been previously identified and enriched from unpreserved timbers of the Mary Rose, demonstrating that biological pathways of iron and sulfur oxidization existed potentially in this wood, before preservation with PEG. This study was designed to establish if the recycled PEG spray system was a reservoir of microorganisms capable of iron and sulfur oxidization during preservation of the Mary Rose. Microbial enrichments derived from PEG impregnated biofilm collected from underneath the Mary Rose hull, were examined to better understand the processes of cycling of iron. X-ray absorption spectroscopy was utilised to demonstrate the biological contribution to production of sulfuric acid in the wood. Using molecular microbiological techniques to examine these enrichment cultures, PEG was found to mediate a shift in the microbial community from a co-culture of Stenotrophomonas and Brevunidimonas sp, to a co-culture of Stenotrophomonas and the iron oxidising Alicyclobacillus sp. Evidence is presented that PEG is not an inert substance in relation to the redox cycling of iron. This is the first demonstration that solutions of PEG used in the conservation of the Mary Rose are promoting the oxidation of ferrous iron in acidic solutions, in which spontaneous abiotic oxidation does not occur in water. Critically, these results suggest PEG mediated redox cycling of iron between valence states in solutions of 75% PEG 200 and 50% PEG 2000 (v/v) at pH 3.0, with serious implications for the future use of PEG as a conservation material of iron rich wooden archaeological artefacts.
  • Vidal-Abarca, C., Lavela, P., Tirado, J., Chadwick, A., Alfredsson, M. and Kelder, E. (2012). Improving the cyclability of sodium-ion cathodes by selection of electrolyte solvent. Journal of Power Sources [Online] 197:314-318. Available at: http://www.dx.doi.org/10.1016/j.jpowsour.2011.09.008.
    A composite material containing orthorhombic Na1.8FePO4F and carbon is prepared by mechanical activation and ceramic procedures. The material is studied in sodium test cells as a potential candidate for sodium-ion battery cathodes. The effect of the solvents in the electrolyte on the electrochemical performance is analysed by X-ray absorption spectroscopy. The structural changes on cycling are small, while the changes in the oxidation state of iron agree with the sodium insertion–extraction processes. The oxidation state is especially affected by the upper limit of the voltage window, and the discharge capacity is strongly affected when using propylene carbonate solvent. Capacity and capacity retention are higher for sodium cells using mixtures of ethylene carbonate and diethyl carbonate as the solvent of NaPF6 electrolytes.
  • Edwards, W., Berko, A., Blacklocks, A., Savin, S. and Chadwick, A. (2012). Ionic transport and structure in doped plastically crystalline solids. Zeitschrift fur Physikalische Chemie [Online] 226:409-420. Available at: http://dx.doi.org/10.1524/zpch.2012.0234.
    There is considerable interest in plastic crystalline electrolytes which have good room temperature ionic conductivities and potential technological applications as membranes for devices such as batteries. Conductivity and X-ray absorption spectroscopy measurements have been used to study succinonitrile (1,2-dicyanoethane) doped with copper(I) and (II) triflate (trifluoromethanesulfonate) and TFSI (bis(trifluoromethane)sulfonimide). The conductivities at room temperature are reasonably good, particularly for Cu(I)TFSI doped at 1 mol%, where the conductivity is � 1�10 -3 S cm -1, which is consistent with previous work on this system. The Cu K-edge EXAFS in 1 mol% doped copper salts show that in all cases, whether Cu(I) or Cu(II), the ion is predominantly in a well-defined and ordered local environment. A tentative model of the conduction process is described that will account for this local structural information; however, the process is clearly complex even in these apparently simple systems. © by Oldenbourg Wissenschaftsverlag, München.
  • Chadwick, A., Berko, A., Schofield, E., Jones, A., Mosselmans, J. and Smith, A. (2012). Application of microfocus x-ray beams from synchrotrons in heritage conservation. International Journal of Architectural Heritage [Online] 6:228-258. Available at: http://dx.doi.org/10.1080/15583058.2010.528825.
    Synchrotron-based techniques are becoming increasingly important in heritage science and the aim of this article is to describe how recently developed microfocus methods can probe the elemental composition, speciation and structure at the micron level in samples from structures. Firstly an outline is given of the major techniques that are used, namely x-ray fluorescence, diffraction and absorption spectroscopy, and the information that they can provide. This is followed by a description of the experimental set-up and procedures. The application of the methods is exemplified by case studies of the degradation of three types of historic structural materials; marble, glass and ship timbers. The results of the studies and their role in developing conservation strategies are described. © 2012 Copyright Taylor and Francis Group, LLC.
  • Canepa, P., Schofield, E., Chadwick, A. and Alfredsson, M. (2011). Comparison of a calculated and measured XANES spectrum of ?-Fe2O3. Physical Chemistry Chemical Physics [Online] 13:12826-12834. Available at: http://dx.doi.org/10.1039/C1CP00034A.
    Comparison and prediction of the experimental XANES spectrum is a good measurement of the quality of the electronic structure calculations employed, and their ability to predict electronic transitions in solids. Here we present a comparison between BLYP + U and hybrid-BLYP calculations regarding the geometric, magnetic and electronic structures of ?-Fe2O3 (hematite). Several values of U and different percentages of Fock-exchange have been screened to see how their contributions affect different properties of hematite, paying particular attention to the electronic structure. To estimate the quality of the various methods the calculated density-of-states were compared to the experimentally collected XANES spectrum of the iron K-edge, providing information about the orbitals describing the conduction band. We find that in agreement with previous studies DFT + U and hybrid-functional simulations can correctly predict the character of the valence band, but only Fock-exchange higher than 30% or U-values equal or larger than 6 eV properly reproduce the order between the tg and e orbitals in the conduction band, and can, therefore, be used to study and predict XANES spectra and electronic transitions in hematite.
  • Nwokeke, U., Chadwick, A., Alcantara, R., Alfredsson, M. and Tirado, J. (2011). Nanocrystalline Fe1-xCoxSn2 solid solutions prepared by reduction of salts in tetraethylene glycol. Journal of Alloys and Compounds [Online] 509:3074-3079. Available at: http://www.dx.doi.org/10.1016/j.jallcom.2010.11.202.
    In an effort to improve the electrochemical performance of tin intermetallic phases as electrode active material for lithium-ion batteries, Fe1?xCoxSn2 solid solutions with x = 0.0, 0.25, 0.3, 0.5, 0.6 and 0.8 were prepared by chemical reduction in tetraethylene glycol. Precise control of the synthesis conditions allowed single-phase nanocrystalline materials to be prepared, with particle diameters of about 20 nm and cubic, nanorods, and U-shaped morphologies. The substitution of iron by cobalt induced a contraction of the unit cell volume. The hyperfine parameters of the 57Fe Mössbauer spectra were sensitive to the Co/Fe substitution and revealed a superparamagnetic behaviour. In lithium cells nanocrystalline Fe1?xCoxSn2 active materials delivered reversible capacities above 500 mAh g?1 that depended on the composition and cycling conditions. The intermediate compositions exhibit better electrochemical performance than the end compositions CoSn2 and FeSn2.
  • Chadwick, A., Berko, A., Schofield, E., Jones, A., Frederick, J., Mosselmans, W. and Smith, A. (2011). How X-rays are helping defeat the effects of micro-organisms in the preservation of Mary Rose. Actualite Chimique [Online]:106-108. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-82255191336&partnerID=40&md5=d8b109a669f813c4b54c767b14161231.
    This article presents a brief overview of the role synchrotron-based X-ray techniques are playing in the preservation of the Mary Rose, a 16th century English warship. The particular problem facing the conservators is the effects of sulfuric acid in the wood formed from sulfur compounds which originate from microbial activity.
  • Lafont, U., Carta, D., Mountjoy, G., Chadwick, A. and Kelder, E. (2010). In Situ Structural Changes upon Electrochemical Lithium Insertion in Nanosized Anatase TiO2. Journal of Physical Chemistry C [Online] 114:1372-1378. Available at: http://dx.doi.org/10.1021/jp908786t.
    The intercalation of lithium in nanosized TiO2 has been studied for its application as an electrode for rechargeable Li-ion batteries. In this paper, we use a synthesis process in order to obtain a low-density anatase TiO2 presenting monocrystalline particles of 7?8 nm. These textural characteristics allow this material to host almost twice as much Li (300 mAh·g?1) than that of a micrometer sized anatase. In this study, in situ X-ray absorption spectroscopy is used to monitor and understand the structural changes that happen upon lithium insertion/removal, leading to a reversible two-phase transition process: TiO2 (I41/amd) ? Li-titanate (Imma) ? Li1TiO2 (I41/amd).
  • Chadwick, A., Berko, A., Blacklocks, A. and Edwards, W. (2010). A combined conductivity and XAS study of plastically crystalline electrolytes. 16th International Conference on Defects in Insulating Materials, ICDIM2008 [Online] 249:12056-12056. Available at: http://dx.doi.org/10.1088/1742-6596/249/1/012056.
    We report a study of the conductivity of LiBr and copper salt doped succinonitrile along with X-ray absorption measurements for the bromide and copper ions. The work shows that the ions are in well-ordered sites for most of the plastic phase and relatively high conductivity is due to a small fraction of the ions which are mobile. © 2010 IOP Publishing Ltd.
  • Berko, A., Smith, A., Jones, A., Schofield, E., Mosselmans, J. and Chadwick, A. (2009). XAS studies of the effectiveness of iron chelating treatments of Mary Rose timbers. Journal of Physics: Conference Series [Online] 190:12147-12147. Available at: http://dx.doi.org/10.1088/1742-6596/190/1/012147.
    The oxidation of sulfur in marine archaeological timbers under museum storage conditions is a recently identified problem, particularly for major artefacts such as historic ships excavated from the seabed. Recent work on the Vasa has stressed the role of iron in catalysing the oxidative degradation of the wood cellulose and the polyethylene glycols used to restore mechanical integrity to the timbers. In developing new treatment protocols for the long term preservation of Henry VIII of England's flagship, the Mary Rose, we are investigating the potential of chelating agents to neutralise and remove the iron products from the ships timbers. We have explored the use of aqueous solutions of chelating agents of calcium phytate, ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA) and ammonium citrate to extract the iron compounds. All of these solutions exhibit some level of iron removal; however the key is to find the most effective concentration at pH of around 7 of the reagent solution, to minimise the treatment time and find the most cost-effective treatment for the whole of the Mary Rose hull. Fe K-edge XAFS data from samples of Mary Rose timbers, before and after treatment by the chelating agents mentioned has been collected. The data collected provide valuable insights into the effectiveness of the treatment solutions. © 2009 IOP Publishing Ltd.
  • Aragon, M., Leon, B., Vicente, C., Tirado, J., Chadwick, A., Berko, A. and Beh, S. (2009). Cobalt oxalate nanoribbons as negative-electrode material for lithium-ion batteries. Chemistry of Materials [Online] 21:1834-1840. Available at: http://dx.doi.org/10.1021/cm803435p.
    Orthorhombic cobalt oxalate dihydrate has been prepared in the form of nanoribbons by a reverse micelles method. The crystallographic structure of the resulting solid differs from the monoclinic massive product. A careful dehydration of the nanocrystals leads to anhydrous cobalt oxalate in which the nanoribbon-shaped particles are preserved and Co2+ ions are located in a centrosymmetric environment. CoC2O4 is used for the first time as high-capacity lithium storage materials with improved rate performance. The anhydrous solids react with lithium, leading to metallic cobalt and lithium oxalate, as shown by XAS and FTIR measurements. The new electrode material displays reversible capacities close to 900 mA h g-1 between 0 and 2 V versus lithium by a novel reaction mechanism which involves cobalt reduction-reoxidation. © 2009 American Chemical Society.
  • Savin, S., Berko, A., Blacklocks, A., Edwards, W. and Chadwick, A. (2008). The applications of X-ray absorption spectroscopy in the study of nanocrystalline materials and electrochemical systems. Comptes Rendus Chimie [Online] 11:948-963. Available at: http://dx.doi.org/10.1016/j.crci.2008.01.016.
    This contribution is based on the presentation given by the authors at the second French-German summer school on electrochemistry and nanotechnology in September 2007. The objective of the article is to describe, by use of examples, the areas of solid-state chemistry and electrochemistry where X-ray absorption spectroscopy can make a special contribution. The case studies that are discussed include the investigation of the microstructure of nanomaterials, the study of electrodes and electrolytes for solid-state battery applications and the location of dopant sites in oxides. The contribution concludes with a look to future developments in the techniques and the implications for the study of problems of materials.
  • Chadwick, A., Newport, R., Pickup, D., Wetherall, K., Moss, R., Jones, M., Goatham, S. and Skinner, T. (2008). Sulfur and iron speciation in recently recovered timbers of the Mary Rose revealed via X-ray absorption spectroscopy. Journal of Archaeological Science [Online] 35:1317-1328. Available at: http://dx.doi.org/10.1016/j.jas.2007.09.007.
    This paper reports the results of an investigation into the mechanisms that have led to the build up of sulfuric acid in the timbers of the Mary Rose, with a particular focus on recently recovered timbers. Measurements have been made by sulfur and iron K-edge X-ray absorption near edge spectroscopy (XANES), X-ray microscopy and by X-ray diffraction (XRD). Results from S K-edge XANES studies reveal that the concentration of highly oxidised S decreases with depth into the timber, from similar to 15 at.% of S at the surface to negligible levels after approximately 50 mm. Fe K-edge XANES reveals little variation with depth in which Fe3+ ions are dominant. This sheds some light on the sulfur oxidation path, and indicates Fe3+ ions are produced by the oxidation mechanisms that are currently underway. XRD studies have identified several mineral components that may form part of the oxidation chain. These are magnetite (Fe3O4), jarosite (KFe3(SO4)(2)(OH)(6)) and calcite (CaCO3).
  • Jiao, F., Hill, A., Harrison, A., Berko, A., Chadwick, A. and Bruce, P. (2008). Synthesis of ordered mesoporous NiO with crystalline walls and a bimodal pore size distribution. Journal of the American Chemical Society [Online] 130:5262-5266. Available at: http://dx.doi.org/10.1021/ja710849r.
    A mesoporous solid with crystalline walls and an ordered pore structure exhibiting a bimodal pore size distribution (3.3 and 11 nm diameter pores) has been synthesized. Previous attempts to synthesize solids with large ordered mesopores by hard templating focused on the preparation of templates with thick walls (the thick walls become the pores in the target materials), something that has proved difficult to achieve. Here the large pores (11 nm) do not depend on the synthesis of a template with thick walls but instead on controlling the microporous bridging between the two sets of mesopores in the KIT-6 template. Such control determines the relative proportion of the two pore sizes. The wall thickness of the 3D cubic NiO mesopore has also been varied. Preliminary magnetic characterization indicates the freezing of uncompensated moments or blocking of superparamagnetism.
  • Lippens, P., Chadwick, A., Weibel, A., Bouchet, R. and Knauth, P. (2008). Structure and chemical bonding in Zr-doped anatase TiO2 nanocrystals. Journal of Physical Chemistry C [Online] 112:43-47. Available at: http://dx.doi.org/10.1021/jp075898u.
    Zirconium-doped anatase TiO2 nanopowders and nanoceramics with particle sizes between 12 and 30 nm were investigated by EXAFS spectroscopy. Furthermore, ab initio calculations based on density functional theory were performed to analyze changes in the electronic structure due to Zr doping. Zr is dissolved on substitutional bulk sites with a slight increase of the bond lengths of the inner coordination shells. The Debye-Waller factors show that the nanocrystallites are highly ordered. There is no indication for defect states or band gap changes with Zr doping.
  • Yaicle, C., Blacklocks, A., Chadwick, A., Perriere, J. and Rougier, A. (2007). Relationship between structure and deposition conditions for CuInO2 thin films. Applied Surface Science [Online] 254:1343-1346. Available at: http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6THY-4PDSBGR-7&_user=125871&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000010239&_version=1&_urlVersion=0&_userid=125871&md5=3ae88c7b6508995470103fbbbe497049.
    CuInO2 thin films were deposited using the Pulsed Laser Deposition technique. The influence of various deposition parameters and mainly the oxygen pressure on the texture, composition and structure of the films is discussed. Films deposited with an oxygen pressure in the 0.2-1 Pa range exhibit the delafossite structure. Higher pressure introduces an increase in the oxygen content leading to a CuInO2.10 composition for the film deposited at 5 Pa and a progressive loss of the delafossite structure. As confirmed by an EXAFS study, the oxygen stoichiometry controls the Cu+/ Cu2+ ratio.
  • Mir, J., Sole, D., Lipp, J., Stephenson, R., Purton, J., Savin, S., Chadwick, A. and O’Dell, L. (2007). Low X-ray energy fluorescence Gas Electron Multiplier (GEM) for XAS studies. IEEE Transactions on Nuclear Science [Online] 54:2637-2641. Available at: http://dx.doi.org/10.1109/TNS.2007.908699.
    X-ray absorption spectroscopy at sub-keV energies dictates the use of detectors that can attain a good signal-to-noise ratio. We report a recent study undertaken at Science and Technology Facilities Council, Daresbury Laboratory to evaluate the performance of a Gas Electron Multiplier (GEM) for this purpose. The main impetus of this study was to investigate the relevant parameters such as the effective gain and energy resolution in the X-ray energy range of 270-930 eV. This study demonstrated that a single stage GEM can sustain effective gains up to 60 000 in a helium-isobutane counter gas mixture at atmospheric pressure. Consequently, high signal-to-noise ratios were achieved (electronic noise similar to 500 electrons r.m.s) thereby permitting adequate X-ray energy resolution.
  • O’Dell, L., Savin, S., Chadwick, A. and Smith, M. (2007). Multinuclear MAS NMR investigation of sol-gel and ball-milled nanocrystalline Ga2O3. Applied Magnetic Resonance [Online] 32:527-546. Available at: http://dx.doi.org/10.1007/s00723-007-0036-x.
    Ga-71 magic-angle spinning (MAS) nuclear magnetic resonance (NMR) has been used to characterize the structural evolution of nanocrystalline Ga2O3 samples prepared by sol-gel and ball-milling techniques. Si-29 and Al-27 MAS NMR have also been used to characterize silica and alumina Zener pinning phases. Ga-71 NMR parameters are reported for the alpha- and beta-Ga2O3 phases, and more tentatively for the delta-Ga2O3 phase. By simulating the octahedrally coordinated gallium NMR line of beta-Ga2O3 using Gaussian distributions in chi(Q), the extent of disorder in the Ga2O3 crystallites has been quantified. The ball-milled samples contain much more inherent disorder than the sol-gel samples in the nano-phase, which was observed from simulations of the Ga-71 MAS NMR spectra. The silica pinning phase produced highly crystalline and densely aggregated nanocrystalline Ga2O3, as well as the smallest nanocrystal sizes
  • Aleman, J., Chadwick, A., He, J., Hess, M., Horie, K., Jones, R., Kratochvil, P., Meisel, I., Mita, I., Moad, G., Penczek, S. and Stepto, R. (2007). Definitions of terms relating to the structure and processing of sols, gels, networks, and inorganic-organic hybrid materials (IUPAC Recommendations 2007). Pure and Applied Chemistry [Online] 79:1801 -1827. Available at: http://dx.doi.org/10.1351/pac200779101801.
    This document defines terms related to the structure and processing of inorganic, polymeric, and inorganic-organic hybrid materials from precursors, through gels to solid products. It is divided into four sections-precursors, gels, solids, and processes- and the terms have been restricted to those most commonly encountered.
    For the sake of completeness and where they are already satisfactorily defined for the scope of this document, terms from other IUPAC publications have been used. Otherwise, the terms and their definitions have been assembled in consultation with experts in the relevant fields. The definitions are intended to assist the reader who is unfamiliar with sol-gel processing, ceramization, and related technologies and materials, and to serve as a guide to the use of standard terminology by those researching in these areas.
  • O’Dell, L., Savin, S., Chadwick, A. and Smith, M. (2007). Structural characterization of SiO2 and Al2O3 zener-pinned nanocrystalline TiO2 by NMR, XRD and electron microscopy. Journal of Physical Chemistry C [Online] 111:1370-13746. Available at: http://dx.doi.org/10.1021/jp0739871.
    Nanocrystalline TiO2 samples were prepared using sol-gel techniques in a pure form and also Zener pinned with either silica or alumina to reduce the growth of the crystallites during the annealing process and to stabilize the anatase phase at high temperatures. These samples were studied using O-17, Al-27, and Si-29 nuclear magnetic resonance (NMR), X-ray diffraction (XRD), and electron microscopy. The silica pinning phase was found to successfully restrict nanocrystal growth as well as stabilize the anatase phase at temperatures up to 800 degrees C. The alumina phase had less of a pinning effect, and it reacted with the TiO2 to form tialite. O-17 NMR relaxation time measurements on enriched samples showed that the presence of the pinning phases also reduced the activation energy for the oxygen ion diffusion mechanism.
  • O’Dell, L., Savin, S., Chadwick, A. and Smith, M. (2007). A Al-27 MAS NMR study of a sol-gel produced alumina: Identification of the NMR parameters of the theta-Al2O3 transition alumina phase. Solid State Nuclear Magnetic Resonance [Online] 31:169-173. Available at: http://dx.doi.org/10.1016/j.ssnmr.2007.05.002.
    Al-27 MAS NMR has been used to study a sol-gel prepared alumina annealed at various temperatures. Two-field simulation of the sample heated to 1200 degrees C confirmed the presence of corundum, as suggested by XRD, and also the presence of nanocrystalline theta-Al2O3. Al-27 MAS NMR chemical shifts, quadrupolar coupling constants and asymmetry parameters are reported for the tetrahedral and octahedral aluminium sites within theta-Al2O3.
  • Chadwick, A., Savin, S., Fiddy, S., Alcantara, R., Lisbona, D., Lavela, P., Ortiz, G. and Tirado, J. (2007). Formation and oxidation of nanosized metal particles by electrochemical reaction of Li and Na with NiCo2O4: X-ray absorption spectroscopic study. Journal of Physical Chemistry C [Online] 111:4636-4642. Available at: http://dx.doi.org/10.1021/jp066417u.
    X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy have been used to investigate the electrochemical reactions of NiCo2O4 in lithium and sodium test cells. Nanosized particles of NiCo2O4 were prepared by the thermal decomposition of a mixed oxalate precursor and used as active electrode material. Ni K and Co K XANES results give evidence of the successive steps in the reduction mechanism of the oxide during the first cell discharge. In a first step NiCo2O4 reacts with lithium and sodium and the reduction of both Ni3+ and Co3+ to the 2+ oxidation state is shown by a peak shift to lower energy values. As a result, sodium oxide or lithium oxide and the transition metal monoxides are formed. Second, metallic products are formed, in which the average coordination numbers of the nearest neighbors for Ni and Co derived from the EXAFS data are 4 and 5, respectively, associated with ca. 1 nm particle size. These novel ultrafine particles are stabilized in the Li2O matrix of the discharged electrodes. Reoxidation of the metallic products up to a divalent state of Ni and Co in the form of monoxides is achieved during the charge process of the electrochemical cells.
  • Chadwick, A. (2007). Transport in defective ionic materials: from bulk to nanocrystals. Physica Status Solidi A [Online] 204:631-641. Available at: http://dx.doi.org/10.1002/pssa.200673780.
    This contribution reviews the current state of knowledge of atomic transport in ionic materials, a dominant theme of the EURODIM Conference series for nearly four decades. The early history of the subject is briefly reviewed followed by the important developments that occurred in the early post-WWII period. That work was mainly based on studies of relatively simple binary ionic systems in the form of single crystals and laid the foundation for much of the current knowledge. An overview is given of more recent work on fast-ion conductors where the materials are generally more complex and the aim is to produce good ionic conductors for applications as electrolyte membranes in batteries and fuel cells. This includes the development of computer simulation techniques that are now an almost essential part of any investigation of ionic transport. Finally, a brief summary is given of transport in nanocrystalline ionic materials (nanoionics) where enhanced ionic conduction has been reported with the potential for significantly improved devices.
  • Blacklocks, A., Chadwick, A., Jackson, R. and Hutton, K. (2007). Investigation into thallium sites and defects in doped scintillation crystals. Physica Status Solidi C [Online] 4:1008-1011. Available at: http://dx.doi.org/10.1002/pssc.200673704.
    Thallium doped caesium iodide, CsI(Tl), and sodium iodide, NaI(Tl) are two of the most efficient scintillators developed and are already widely used for radiation detection and imaging applications. Their use in fast imaging applications however has been hindered by a long lasting high level of afterglow - the percentage of the luminescence pulse remaining a short time after excitation. Very little is known about the point defects in these crystals, such as structure and concentrations, and the first step to understanding the causes of the afterglow is to understand the nature of the defects responsible for the scintillation. In this paper the local structure of the thallium activator ion has been investigated via EXAFS spectroscopy and some basic intrinsic defects calculated using the General Utility Lattice Program (GULP).
  • Page, K., Palgrave, R., Parkin, I., Wilson, M., Savin, S. and Chadwick, A. (2007). Titania and silver-titania composite films on glass-potent antimicrobial coatings. Journal of Materials Chemistry [Online] 17:95-104. Available at: http://dx.doi.org/10.1039/b611740f.
    Titania (anatase) and Ag-doped titania (anatase) coatings were prepared on glass microscope slides by a sol - gel dip-coating method. The resultant coatings were characterised by X-ray diffraction, X-ray absorption near edge structure (XANES), Raman, scanning electron microscopy (SEM), wavelength dispersive X-ray (WDX) analysis, X-ray photoelectron spectroscopy (XPS) and UV-vis techniques and shown to consist of anatase with ca. 0.2 - 1 atom% Ag2O. Photocatalytic activity of the coatings was determined by photomineralisation of stearic acid, monitored by FT-IR spectroscopy. Photocatalytically-active coatings were screened for their antibacterial efficacy against Staphylococcus aureus (NCTC 6571), Escherichia coli ( NCTC 10418) and Bacillus cereus (CH70-2). Ag-doped titania coatings were found to be significantly more photocatalytically and antimicrobially active than a titania coating. No antimicrobial activity was observed in the dark - indicating that silver ion diffusion was not the mechanism for antimicrobial action. The mode of action was explained in terms of a charge separation model. The coatings also demonstrated significantly higher activity against the Gram-positive organisms than against the Gram-negative. The Ag2O - TiO2 coating is a potentially useful coating for hard surfaces in a hospital environment due to its robustness, stability to cleaning and reuse, and its excellent antimicrobial response.
  • Savin, S., Chadwick, A., O’Dell, L. and Smith, M. (2007). Characterisation of nanocrystalline magnesium oxide by X-ray absorption spectroscopy. ChemPhysChem [Online] 8:882-889. Available at: http://dx.doi.org/10.1002/cphc.200600750.
    There are numerous methods of preparing nanocrystalline materials.
    Magnesium oxide is an ideal model system on which to
    probe the relation of the preparative route and the microstructure.
    Using X-ray absorption spectroscopy (XAS) we show that
    the sol-gel route can be used to prepare highly crystalline material
    provided there is careful control of the calcination conditions.
    In the present work this is achieved by calcining at high temperatures
    (at least 800 8C). However, this results in grain growth that
    can be prevented by the addition of a pinning agent, SiO2,
    during the preparation of the sol. The pinned samples maintain
    a particle size of 11 nm even after calcining at 1000 8C. Ball-milling
    is a common method of preparing nanocrystalline oxides,
    however the present work shows that this produces a significant
    fraction of amorphous material, the fraction increasing with decreasing
    grain size (e.g. 30% for a grain size of 23 nm).
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