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Browsing by Author "Peterson, VK"

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Adsorption of CO2 and CD4 in UiO-66: a combination of neutron diffraction and modelling
(Australian Institute of Physics, 2015-02-06) Chevreau, H; Laing, W; Kearley, GJ; Duyker, SG; D’Alessandro, DM; Peterson, VK
Over the last twenty years, tremendous progress has been achieved in the field of Metal Organic Frameworks. Among these materials, the zirconium terephthalate UiO-66(Zr) [1] has attracted a growing attention because of its interesting thermal, chemical and water stability and has shown to be a promising material for the separation of CO2/CH4 gas mixtures. In order to get a better understanding of its sorption behavior towards CO2 and CH4, a Neutron Powder Diffraction (NPD) investigation of UiO-66 loaded with sequential doses of CO2 and CD4 has been carried out on the High Resolution Powder Diffractometer instrument “Echidna” at the OPAL reactor (ANSTO, Sydney). In total, three adsorption sites for CO2 and three adsorption sites for CD4 within the UiO- 66(Zr) have been located by neutron powder-diffraction then characterised by a combination of first-principles Density Functional Theory (DFT) calculations and Quantum Atoms In Molecules (QTAIM) theory. An example of the first CO2 adsorption site is given in figure 1.
Advancing energy technologies by understanding material function using neutron scattering and computational methods
(International Conference on Neutron Scattering, 2017-07-11) Peterson, VK
Functional materials form the central part of many important energy technologies. A material’s atomic structure and dynamics underpin performance characteristics, and the characterization of these is central to technology advancement. The functional materials at the heart of energy devices often reversibly host charge or energy carriers, and characterization focuses on understanding how these guests are accommodated by the host material. Neutron scattering has made important contributions to this understanding, and is naturally complemented by first-principles calculations, with the combination particularly powerful for studying energy materials. Ideally, such studies will probe the material’s functional mechanism and be performed during function within a device or during the material’s response to external stimuli ( operando and in situ studies), as analyses of a functional material at equilibrium can yield misleading or incomplete results. Functional materials analysis is therefore greatly benefited by modern high-speed instrumentation, which allows the rapid collection of data and real-time information concerning the functioning/responding material to be gained. This presentation will give examples of neutron scattering and first-principles computational analysis of functional materials for energy systems under equilibrium and non-equilibrium conditions. Examples will include rechargeable battery electrodes and sorbent materials used for the separation and storage of energy-relevant gases.
Alkali metal dynamics in the β-pyrochlores A0s206 (A = K, Rb, Cs) and their prospects as thermoelectric materials
(Australian Institute of Nuclear Science and Engineering (AINSE), 2012-11-07) Shoko, E; Peterson, VK; Kearley, GJ
The β-pyrochlores A0s206 (A = K, Rb, Cs)are extensively studied because of their superconducting properties that are believed to be linked to the rattling modes of the alkali metals. The rattling of small atoms encaged in large cavities has been mown to be important for the thermoelectric performance of both clathrates and skutterudites, and fuels our interest in the osmates. The vibrational dynamics of the K atom in KOs206, differs significantly from those of Rb and Cs in their respective pyrochlores and a complex low-energy signature was recently observed using inelastic neutron scattering (INS). To gain insight into the dynamics of the alkai metais in this system, we studied these materials using ab initio molecular dynamics (MD) simulations validated against experimental INS spectra. Combining the results of MD simulations with phonon dispersion curves, calculated from ab initio lattice dynamics (LD) enabled the prediction of thermoelectric properties for these materials using the Boltzmann transport equation. This talk will discuss the alkali metal dynamics in terms of their relevance in the potential development of this class of materials for thermoelectric applications.
Anisotropic thermal and guest-induced responses of an ultramicroporous framework with rigid linkers
(John Wiley & Sons, Inc, 2018-02-16) Auckett, JE; Duyker, SG; Izgorodina, EI; Hawes, CS; Turner, DR; Batten, SR; Peterson, VK
The interdependent effects of temperature and guest uptake on the structure of the ultramicroporous metal–organic framework [Cu3(cdm)4] (cdm=C(CN)2(CONH2)−) were explored in detail by using in situ neutron scattering and density functional theory calculations. The tetragonal lattice displays an anisotropic thermal response related to a hinged “lattice-fence” mechanism, unusual for this topology, which is facilitated by pivoting of the rigid cdm anion about the Cu nodes. Calculated pore-size metrics clearly illustrate the potential for temperature-mediated adsorption in ultramicroporous frameworks due to thermal fluctuations of the pore diameter near the value of the target guest kinetic diameter, though in [Cu3(cdm)4] this is counteracted by a competing contraction of the pore with increasing temperature as a result of the anisotropic lattice response. © 2018 Wiley-VCH Verlag GmbH & Co.
Anomalous lattice parameter increase in alkali earth aluminium substituted tungsten defect pyrochlores
(Elsevier, 2009-03) Thorogood, GJ; Kennedy, BJ; Peterson, VK; Elcombe, MM; Kearley, GJ; Hanna, JV; Luca, V
The structures of the defect pyrochlores AAl(0.33)W(1.67)O(6) where A = K, Rb or Cs have been investigated using X-ray and neutron powder diffraction methods as well as the ab initio modelling program VASP The three cubic pyrochlores exhibit a non-linear increase in lattice parameter with respect to ionic radius of the A cation as a consequence of displacive disorder of the A-type cations. Solid state Al-27 MAS NMR studies of this pyrochlore system reveal shifts in the delta-21-22 ppm range that are indicative of pseudo-5 coordinate Al environments and emanate frorn distorted Al octahedral with one abnormally long Al. O bond. Solid state K-39, Rb-85, Rb-87 and Cs-133 MAS and static NMR Studies reflect the local cation disorder demonstrated in the structural Studies. © 2008, Elsevier Ltd.
Atomic-scale explorations of stimulus-responsive framework properties in an ultramicroporous gas sorbent
(Society of Crystallographers in Australia and New Zealand, 2017-12-03) Auckett, JE; Duyker, SG; Izgorodina, EI; Hawes, CS; Turner, DR; Batten, SS; Peterson, VK
Functional microporous materials capable of efficiently separating and/or storing gases at noncryogenic temperatures are sought for a wide variety of important industrial applications, including pre- and post-combustion carbon capture, hydrogen fuel storage, and the purification of component gases from air. Understanding the atomic-scale interactions between the host material and guest species under variable operating conditions is essential for obtaining information about adsorption and separation mechanisms, which can in turn be used to design better sorbents targeted at specific applications. The ultramicroporous metal-organic framework [Cu3(cdm)4] (cdm = C(CN)2CONH2 -) was recently reported to exhibit moderately selective adsorption of CO2 over CH4, along with excellent exclusion of elemental gases such as H2 and N2 [1]. Although the very small pore diameter (3–4 Å) results in unpromisingly slow diffusion dynamics, its close similarity to the kinetic diameters of many small gas molecules [2] also raises the prospect of altering the gas sorption and selectivity characteristics of the material via minor structural modifications, such as might be introduced by changing the temperature and/or guest concentration during sorbent operation under industrially relevant conditions. Using a combination of in situ neutron scattering experiments and density functional theory-based calculations, we examine in detail the interplay between lattice shape, pore size, temperature, and CO2 concentration in [Cu3(cdm)4]. The rare and interesting fundamental property of areal negative thermal expansion (NTE) in [Cu3(cdm)4] is attributed to a new variation of a well-known NTE mechanism, and is triggered by dynamic motions of the rigid cdm ligand within the constraints of the complicated framework topology. Although the thermal response of the pore diameter is surprisingly insignificant due to competition between multiple effects, the potential for similar materials to exhibit temperature induced changes in adsorption properties is clearly demonstrated. This study illustrates the breadth and depth of information that can be obtained by combining the power of experimental and theoretical characterisation in an approach that is generally applicable to crystalline sorbent systems.
Atomic-scale understanding of CO2 adsorption processes in metal-organic framework (MOF) materials using neutron scattering and ab-initio calculations
(Australian Institute of Physics, 2016-02-04) Auckett, JE; Peterson, VK; Duyker, SG
The dependence of the industrialised world on fossil-fuel energy generation technologies and consequent increase in atmospheric CO2 concentrations has been blamed for emerging adverse climate effects, including an increase in global mean temperatures. Until renewable, carbon-free energy sources can be efficiently harnessed to meet the world’s energy needs, interim measures are sought to suppress the atmospheric release of CO2 from traditional coal and natural gas combustion processes. Microporous materials such as zeolites and metal-organic frameworks (MOFs) are therefore being investigated for the separation and capture of CO2 at various stages of the combustion cycle. MOFs represent one of the most promising classes of materials for this application, offering unrivalled tunability of structural and chemical characteristics via the substitution of metals and choice and functionalisation of ligands. In order for a MOF to be rationally tuned for improved performance, the nature of the interactions between the host framework and guest molecules must be well-understood at the atomic level. Our research targets this detailed understanding of MOFs using neutron scattering and computational methods. We are currently investigating several MOFs which display unexpected sorption properties such as “reverse sieving” – that is, selectively absorbing larger gas molecules while rejecting smaller ones – and unusual lattice expansion effects. Using in situ diffraction to locate the preferred binding sites of guest molecules in the framework, inelastic neutron scattering to probe system dynamics, and density functional theory-based molecular dynamics simulations to validate and interpret our experimental results, we are able to gain detailed information about the mechanisms of gas uptake and diffusion in these exciting new MOF materials.
Batteries & supercaps: in situ and operando methods for energy storage and conversion
(John Wiley & Sons, Inc, 2021-10-22) Peterson, VK; Stievano, L
Take a close look: This Special Collection is devoted to in situ and (in) operando methods developed and used for studying materials applied to electrochemical storage devices. © 2021 Wiley-VCH
Br-doped Li4Ti5O12 and composite TiO2 anodes for Li-ion batteries: synchrotron x-ray and in situ neutron diffraction studies
(John Wiley & Sons, Inc, 2011-09-01) Du, GD; Sharma, N; Peterson, VK; Kimpton, JA; Jia, DZ; Guo, ZP
Synchrotron X-ray diffraction data were used to determine the phase purity and re-evaluate the crystal-structure of Li4Ti5O12-xBrx electrode materials (where the synthetic chemical inputs are x = 0.05, 0.10 0.20, 0.30). A maximum of x′ = 0.12 Br, where x′ is the Rietveld-refined value, can be substituted into the crystal structure with at least 2% rutile TiO2 forming as a second phase. Higher Br concentrations induced the formation of a third, presumably Br-rich, phase. These materials function as composite anodes that contain mixtures of TiO2, Li4Ti5O12-xBrx, and a Br-rich third, unknown, phase. The minor quantities of the secondary phases in combination with Li4Ti5O12-xBrx where x′ ∼ 0.1 were found to correspond to the optimum in electrochemical properties, while larger quantities of the secondary phases contributed to the degradation of the performance. In situ neutron diffraction of a composite anatase TiO2/Li4Ti5O12 anode within a custom-built battery was used to determine the electrochemical function of the TiO2 component. The Li4Ti5O12 component was found to be electrochemically active at lower voltages (1.5 V) relative to TiO2 (1.7 V). This enabled Li insertion/extraction to be tuned through the choice of voltage range in both components of this composite or in the anatase TiO2 phase only. The use of composite materials may facilitate the development of multi-component electrodes where different active materials can be cycled in order to tune power output. Copyright © 2011 Wiley-VCH Verlag GmbH & Co.
Bulk and surface properties regulation of single/double perovskites to realize enhanced oxygen evolution reactivity
(John Wiley & Sons, Inc, 2020-04-06) Sun, HS; Hu, B; Guan, DQ; Hu, ZW; Fei, LS; Li, MR; Peterson, VK; Lin, HJ; Chen, CT; Ran, R; Zhou, W; Shao, ZP
Perovskite-based oxides have emerged as promising oxygen evolution reaction (OER) electrocatalysts. The performance is closely related to the lattice, electronic, and defect structure of the oxides, which determine surface and bulk properties and consequent catalytic activity and durability. Further, interfacial interactions between phases in a nanocomposite may affect bulk transportation and surface adsorption properties in a similar manner to phase doping except without solubility limits. Herein, we report the development of a single/double perovskite nanohybrid with limited surface self-reconstruction capability as an OER electrocatalyst. Such superior performance arises from a structure that maintains high crystallinity post OER catalysis, in addition to forming an amorphous layer following the self-reconstruction of a single perovskite structure during the OER process. In situ X-ray absorption near edge structure spectroscopy and high-resolution synchrotron-based X-ray diffraction reveal an amorphization process in the hybrid single/double perovskite oxide system that is limited in comparison to single perovskite amorphization, ensuring high catalytic activity. © 2020 Wiley-VCH Verlag GmbH & Co
Calcium substitution to improve the total ionic conductivity of the Li3/8Sr7/16Ta3/4Hf1/4O3 perovskite-type electrolyte
(Elsevier, 2023-11-01) Bertrand, M; Groleau, L; Bibienne, T; Rousselot, S; Liu, X; Chi, M; Yang, FZT; Peterson, VK; Schmid, S; Dollé, M
We report novel calcium-substituted perovskite-type solid state electrolyte with nominal composition Li0.344Sr0.433Ca0.02Ta3/4Hf1/4O3, which we compare with Li3/8Sr7/16Ta3/4Hf1/4O3. The compounds were synthesized via solid-state reaction and studied by X-ray and neutron powder diffraction and electrochemical impedance spectroscopy. Neutron powder diffraction allowed the Li position in the structure to be accurately determined. Calcium-substituted phase showed higher Li-ion conductivity than the analogous calcium-free phase obtained with our synthesis method. High total Li-ion conductivities of 3.6 ± 1.0 × 10−4 S cm−1 (Ea = 431 meV) at 30 °C were reached for calcium-substituted phase, and both bulk and grain-boundary conductivities increased compared to that of the calcium-free phase. The same experiment was conducted on Li0.344Sr0.433Ca0.02Ta3/4Zr1/4O3 and led to the same conclusion compared to Li3/8Sr7/16Ta3/4Zr1/4O3. Elemental analysis by energy-dispersive X-ray (EDX) of Li0.344Sr0.433Ca0.02Ta3/4Hf1/4O3 showed the formation of an intermediary phase at grain boundaries, which contained essentially strontium, calcium, and oxygen. To better understand the increased bulk conductivity, neutron diffraction was performed on Li0.344Sr0.433Ca0.02Ta3/4Hf1/4O3. The results demonstrate the importance of understanding and controlling the grain boundary composition, as much as the bulk composition, to improve the total ionic conductivity of solid electrolytes. © 2023 Elsevier B.V. All rights reserved.
Capacity enhancement of the quenched Li-Ni-Mn-Co oxide high-voltage Li-ion battery positive electrode
(Elsevier, 2017-03-23) Jena, A; Lee, CH; Pang, WK; Peterson, VK; Sharma, N; Wang, CC; Song, YF; Lin, CC; Chang, H; Liu, RS
Li-rich metal oxides, regarded as a high-voltage composite cathode, is currently one of the hottest positive electrode material for lithium-ion batteries, due to its high-capacity and high-energy performance. The crystallography, phase composition and morphology can be altered by synthesis parameters, which can influence drastically the capacity and cycling performance. In this work, we demonstrate Li1.207Ni0.127Mn0.54Co0.127O2, obtained by a co-precipitation method, exhibits super-high specific capacity up to 298 mAh g−1 and excellent capacity retention of ∼100% up to 50 cycles. Using neutron powder diffraction and transmission X-ray microscopy, we have found that the cooling-treatments applied after sintering during synthesis are crucially important in controlling the phase composition and morphology of the cathodes, thereby influencing the electrochemical performance. Unique spherical microstructure, larger lattice, and higher content of Li-rich monoclinic component can be achieved in the rapid quenching process, whereas severe particle cracking along with the smaller lattice and lower monoclinic component content is obtained when natural cooling of the furnace is applied. Combined with electrochemical impedance spectra, a plausible mechanism is described for the poorer specific capacity and cycling stability of the composite cathodes. © 2017 Elsevier Ltd.
Cation disorder in NaW2O6+δ·nH2−zO post-ion exchange with K, Rb, Sr, and Cs
(Pergamon-Elsevier Science Ltd, 2011-06-01) Thorogood, GJ; Kennedy, BJ; Avdeev, M; Peterson, VK; Hanna, JV; Luca, V
The structure of the defect pyrochlore NaW2O6+delta center dot nH(2-z)O after ion exchange with K, Rb, Sr or Cs for Na has been investigated using thermal analysis, solid-state nuclear magnetic resonance, laboratory X-ray and neutron diffraction methods. Neutron diffraction studies show that both the A-type cations (Na+, K+, Rb+, and/or Cs+) and the water molecules reside within the channels that form in the 111 direction of the W2O6 framework and that these strongly interact. The analytical results suggest that the water and A-type cations compete for space in the tunnels within the W2O6 pyrochlore framework, with the total number of water molecules and cations being approximately constant in the six samples investigated. The interplay between the cations and water explains the non-linear dependence of the a lattice parameter on the choice of cation. It appears that the ion-exchange capacity of the material will be controlled by the amount of water initially present in the sample. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.
Cation order/disorder and local structures in alkaline earth pyrochlores
(International Union of Crystallography (IUCr), 2008-08-23) Thorogood, GJ; Kennedy, BJ; Peterson, VK; Elcombe, MM; Kearley, GJ; Hanna, JV
Materials that form the A2-yB2O7-x pyrochlore structure have various applications including use as catalysts, fuel cells, piezoelectrics, ferroelectric devices and ferro-magnets; have a wide range of electrical and ionic conductivities, including metallic, semi and super; can be used in nuclear-waste immobilisation due to radiation toughness, and have ion exchange properties. The degree of disorder of the A-cation is important and may play the major role in the effectiveness of these materials ion exchange properties; and contribute to the high relative permittivities displayed by (Bi,Zn)2(Zn,Nb)2O7. Previous Neutron and X-ray diffraction studies suggest that the disorder involves displacement of the A-cation along the six <112> or <110> directions. Our observation of diffuse scattering in electron diffraction patterns of CsTi0.5W1.5O6 pyrochlores suggests there are strong local correlations among the disordered ions. Movement of O at 48f away from 0.375 reduces the interaction between the two networks and so may increase the amount of disorder of the A-cation. The structures of the defect pyrochlores AAl0.33W1.67O6 where A= K, Rb or Cs have been investigated using an array of advanced structural probes; X-ray and neutron diffraction methods, NMR spectroscopy as well as the ab-initio modeling using VASP. The structures do not show a simple correlation between the radius of the A-type cation and the cubic lattice parameter. Our structural studies suggest that this may reflect the degree of local disorder of the A-cation. The results of these studies will be presented in this presentation. © 2008 International Union of Crystallography
Chromium ion pair luminescence: a strategy in broadband near- infrared light-emitting diode design
(American Chemical Society, 2021-11-04) Rajendran, V; Fang, MH; Huang, WT; Majewska, N; Lesniewski, T; Mahlik, S; Leniec, G; Kazmarek, SM; Pang, WK; Peterson, VK; Lu, KM; Chang, H; Liu, RS
Portable near-infrared (NIR) light sources are in high demand for applications in spectroscopy, night vision, bioimaging, and many others. Typical phosphor designs feature isolated Cr3+ ion centers, and it is challenging to design broadband NIR phosphors based on Cr3+–Cr3+ pairs. Here, we explore the solid-solution series SrAl11.88–xGaxO19:0.12Cr3+ (x = 0, 2, 4, 6, 8, 10, and 12) as phosphors featuring Cr3+–Cr3+ pairs and evaluate structure–property relations within the series. We establish the incorporation of Ga within the magentoplumbite-type structure at five distinct crystallographic sites and evaluate the effect of this incorporation on the Cr3+–Cr3+ ion pair proximity. Electron paramagnetic measurements reveal the presence of both isolated Cr3+ and Cr3+–Cr3+ pairs, resulting in NIR luminescence at approximately 650–1050 nm. Unexpectedly, the origin of broadband NIR luminescence with a peak within the range 740–820 nm is related to the Cr3+–Cr3+ ion pair. We demonstrate the application of the SrAl5.88Ga6O19:0.12Cr3+ phosphor, which possesses an internal quantum efficiency of ∼85%, a radiant flux of ∼95 mW, and zero thermal quenching up to 500 K. This work provides a further understanding of spectral shifts in phosphor solid solutions and in particular the application of the magentoplumbites as promising next-generation NIR phosphor host systems. © 2021 American Chemical Society
A combined DFT and NPD approach to determine the structure and composition of the ε-phase of tungsten boride
(Elsevier, 2023-10-15) Setayandeh, SS; Stansby, JH; Obbard, EG; Brand, MI; Miskovic, DM; Laws, KJ; Peterson, VK; Astbury, JO; Wilson, CL; Irukuvarghula, S; Burr, PA
The ε-phase of tungsten boride, conventionally labelled as W2B5, has been identified as a promising candidate for shielding application in spherical tokamak fusion reactors. However, further research has been hindered by a lack of agreement on the structure and even composition of the ε-phase. Here, we identify the stable crystal structure and stoichiometry range of ε tungsten borides through a combination of ab initio simulations and neutron diffraction of isotopically enriched samples. We considered the ability to accommodate hypo-stoichiometry in six published structures of the ε phase. Chemical disorder was modelled using configurational ensembles to account for entropy of non-stoichiometry. We show that two W2B4-x structures (with x=∼0.25 − 0.5), with space group symmetry P63/mmc and P63/mcm, appear to be thermodynamically stable. These candidate compounds have 6.2 − 7.8 at.% less B than the W2B5 composition reported in exiting phase diagrams. We confirm these findings by means of neutron powder diffraction, performed on 11B-enriched arc-melted and crushed samples. Rietveld refinement using the neutron data shows the ε-phase to be better described as W2B3.60(2) (P63/mcm), in keeping with density functional theory (DFT) calculations. Linear change in DFT-derived lattice parameters of the candidates for the ε-phase proposes a simple model to assess the tungsten boride composition by measuring the lattice parameter (e.g. by X-ray diffraction. The simulations also reveal that the material can accommodate a range of stoichiometric variations (via B vacancies) with relatively small stored energy, which is a desirable feature for neutron shielding application. © 2023 The Authors. Published by Elsevier Ltd on behalf of Acta Materialia Inc. Open Access CC-NC-ND
A comparative study of SrCo0.8Nb0.2O3−δ and SrCo0.8Ta0.2O3−δ as low-temperature solid oxide fuel cell cathodes: effect of non-geometry factors on the oxygen reduction reaction
(Royal Society of Chemistry, 2015-11-11) Li, MR; Zhou, W; Peterson, VK; Zhao, MW; Zhu, ZH
The oxygen reduction reaction (ORR) activity of cathodes has to be improved to realize the low-temperature operation of solid-oxide fuel cells (SOFCs). Whilst geometric factors are conventionally accepted to influence the ORR activity of perovskite cathodes, other factors may also contribute and therefore need to be explored. Here, we substituted 20% niobium and tantalum which have similar ionic radii into strontium cobaltites to obtain the two perovskite oxides SrCo0.8Nb0.2O3−δ (SCN20) and SrCo0.8Ta0.2O3−δ (SCT20), respectively. Our study of the isostructural SCN20 and SCT20 allows geometric effects to be separated from other factors, and we observe better cathode performance of SCT20 cathode, which may be related to the lower electronegativity of Ta5+, thus resulting in higher oxygen surface exchange kinetics and diffusivity as compared with Nb5+. © Royal Society of Chemistry 2015
Comparison of the so-called CGR and NCR cathodes in commercial lithium-ion batteries using in situ neutron powder diffraction
(Cambridge University Press, 2014-12-18) Alam, M; Hanley, TL; Pang, WK; Peterson, VK; Sharma, N
The evolution of the 003 reflection of the layered Li(Ni,Co,Mn)O2 (CGR) and Li(Ni,Co,Al)O2 (NCR) cathodes in commercial 18650 lithium-ion batteries during charge/discharge were determined using in situ neutron powder diffraction. The 003 reflection is chosen as it is the stacking axis of the layered structure and shows the largest change during charge/discharge. The comparison between these two cathodes shows that the NCR cathode exhibits an unusual contraction near the charged state and during the potentiostatic step, where the potentiostatic step is recommended by the manufacturer. This feature is not shown to the same degree by the CGR cathode. The behavior is likely related to the compositions of these cathodes, the amount of Li/Ni site mixing and the presence of Al or Mn. © 2014 International Centre for Diffraction Data. Published by Cambridge University Press
Comparison of thermal stability in MAX 211 and 312 phases
(Insitute of Physics, 2010-05-03) Pang, WK; Low, IM; O'Connor, BH; Studer, AJ; Peterson, VK; Sun, ZM; Palmquist, JP
The susceptibility of four MAX phases (Ti 2 AlC, Cr 2 AlC, Ti 3 AlC 2 , and Ti 3 SiC 2 ) to high-temperature thermal dissociation in vacuum has been investigated using in-situ neutron diffraction. In high vacuum, these phases decomposed above 1400Â°C through the sublimation of M and A elements, forming a surface coating of MC. The apparent activation energies for the decomposition of sintered Ti 3 SiC 2 , Ti 3 AlC 2 , and Ti 2 AlC were determined to be 179.3, -71.9, and 85.7 kJ mol âˆ’1 , respectively. The spontaneous release of Ti 2 AlC and TiC from de-intercalation during decomposition of Ti 3 AlC 2 resulted in a negative activation energy.© 2010, Insitute of Physics
Composition and temperature dependent structural investigation of perovskite-type sodium-ion solid electrolyte series Na1/2-xLa1/2-xSr2xZrO3
(Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Yang, F; Schmid, S; Peterson, VK
The development of new solid electrolytes is becoming increasingly important, e.g. in rechargeable batteries for electric vehicles, where current organic electrolytes cause major safety concerns. The ABO3 perovskite metal oxides have shown excellent lithium and sodium ion conductivity owing to their stability and structural flexibility. This has led to the development of several perovskite-type solid electrolytes such as Li3xLa2/3- xTiO3 and Na1/2-xLa1/2-xSr2xZrO3, which have shown high ionic conductivity. The Na1/2-xLa1/2-xSr2xZrO3 perovskite-type sodium-ion solid electrolyte system was recently published by Zhao et al. [1] with the x=1/6 member, i.e. Na1/3La1/3Sr1/3ZrO3, found to have the highest ionic conductivity. The structure was reported to adopt a cubic crystal system with the space group P213. However, this is highly unlikely as both theoretical end members of the series, Na1/2La1/2ZrO3 and SrZrO3, have orthorhombic symmetry[2, 3]. Given the high ionic conductivity reported for the system, it is important to determine its structure reliable and with the best available data. Using neutron and X-ray powder diffraction data we have been able to confirm that the symmetry across the series is lowered to orthorhombic indeed. Variable temperature neutron powder diffraction data collected for the x=1/6 member of the system from room temperature to 1100 ◦C helped to identify a structural phase transition from orthorhombic to tetragonal symmetry at 800◦C. © The Authors.

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