Browsing by Author "Elcombe, MM"
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- ItemAnomalous 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, VThe 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.
- ItemApplication of small-angle scattering to study the effects of moisture content on a native soy protein(Wiley-Blackwell, 2008-06) Kealley, CS; Elcombe, MM; Wuhrer, R; Gilbert, EPThe nano-and microstructure of glycinin, a soybean protein, has been investigated as a function of moisture for moisture contents between 4 and 21 wt%. Glycinin exhibits peaks in the small-angle region whose positions show minimal change with X-rays for samples up to 13% moisture. However, the use of neutron scattering, and the associated enhancement in contrast, results in the Bragg peaks being well resolved up to higher moisture contents; the associated shift in peak positions between 4 and 21% moisture are consistent with the expansion of a hexagonal unit cell as a function of moisture content. A Porod slope of similar to-4 indicates that the interface between the 'dry' protein powder and the surrounding medium at a length-scale of at least 3 mm down to similar to 20 nm is smooth and sharp. Scanning electron microscopy indicates that the powders, with low moisture content, have a porous appearance, with the porosity decreasing and microstructure expanding as the moisture content increases. © 2008, Wiley-Blackwell.
- ItemCation 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, JVMaterials 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
- ItemCharacterization of nanocrystalline materials using different diffraction techniques(International Community for Composites Engineering, 2008-07-20) Kamarulzaman, N; Bustam, MA; Blagojevic, N; Elcombe, MM; Blackford, MG; Avdeev, M; Arof, AKNo abstract available.
- ItemCoexistence of ferroelectricity and magnetism in transition-metal-doped n = 3 aurivillius phases(Institute of Physics, 2008-01-16) Sharma, N; Kennedy, BJ; Elcombe, MM; Liu, Y; Ling, CDMagnetic-cation-doped three-layer Aurivillius phases Bi2-xSr2+x(Nb/Ta)(2+x)M1-xO12, x approximate to 0.5 and M = Ru4+, Ir4+ or Mn4+, are shown to have the same orthorhombic space group symmetry and similar dielectric and ferroelectric properties as their (non-magnetic) ferroelectric parent compounds Bi2-xSr2+xNb2+xTi1-xO12, x = 0, 0.5. The magnetic-cation-doped phases also show evidence for short-range ferromagnetic (M = Mn) and antiferromagnetic (M = Ru and Ir) exchange, demonstrating the potential of these naturally layered phases as templates for multiferroic (magnetoelectric) materials. © 2008, Institute of Physics
- ItemComposition- and temperature-dependent phase transitions in 1:3 ordered perovskites Ba4-xSrxNaSb3O12(Elsevier, 2007-11) Zhou, QD; Kennedy, BJ; Elcombe, MM; Withers, RLA series of 25 members of the 1:3 ordered perovskite family of the type Ba4-xSrxNaSb3O12 has been synthesized and their structures determined using synchrotron X-ray and neutron powder diffraction techniques. At room temperature the sample Ba4NaSb3O12 has a cubic structure in space group Im (3) over barm with a = 8.2821(1) angstrom, where the Na and Sb cations are ordered in the octahedral sites but there is no tilting of the (Na/Sb)O-6 octahedra. As the average size of the A-site cation decreases, through the progressive replacement of Ba by Sr, tilting of the octahedra is introduced firstly lowering the symmetry to tetragonal in P4/mnc then to orthorhombic in Cmca and ultimately a monoclinic structure in P2(1)/n as seen for Sr4NaSb3O12 with a = 8.0960(2) angstrom, b = 8.0926(2) angstrom, c = 8.1003(1) angstrom and β = 90.016(2)degrees. The powder neutron diffraction studies show that the orthorhombic and tetragonal phases in Cmca and P4/mnc co-exist at room temperature for samples with x between 1.5 and 2. © 2007, Elsevier Ltd.
- ItemCoupled Li1+/Nb5+ and O2-/F- ordering on the Na and Cl sites of the average NaCl structure of Li4NbO4F(Elsevier, 2009-05) Norén, L; Withers, RL; Goossens, DJ; Elcombe, MM; Kearley, GJThe average, as well as the cation and anion 'disordered', crystal Structure of Li4NbO4F has been carefully investigated via coupled neutron and X-ray powder diffraction studies as well as via electron diffraction studies. The existence of a spectacular highly structured diffuse intensity distribution in the latter provides strong evidence for coupled Li1+/Nb5+ and O2-/F- ordering on the Na and Cl sites of the average NaCl structure of Li4NbO4F. Bond valence sum calculations have been used to investigate local crystal chemistry as well as to Suggest plausible local crystal chemical constraints while ab initio DFT based theoretical calculations of a 2 x 2 x 2 supercell have been carried Out in order to provide additional insight into the local crystal chemistry of this compound. © 2009, Elsevier Ltd.
- ItemCrystal chemistry of the alkaline-earth apatites A(10)(PO4)(6)CuxOy(H)(z) (A = Ca, Sr and Ba).(Royal Society of Chemistry, 2009-06-17) Baikie, T; Ng, GMH; Madhavi, S; Pramana, SS; Blake, K; Elcombe, MM; White, TJThe crystal chemistry of the cuprate apatites A(4)(I)A(6)(II)(PO4)(6)CuxOy(H)(z) (A = Ca, Sr and Ba) was investigated by powder X-ray (PXRD) and neutron diffraction (PND) and X-ray photoelectron spectroscopy (XPS). The refined crystal structures confirmed earlier X-ray diffraction studies that showed copper resides in the apatite channels and additionally, located hydrogen. For all materials copper is primarily divalent (Cu2+) but in the calcium and strontium analogues co-exists with minor Cu3+. This is in contrast with a previous work where Cu1+ and Cu2+ were reported. © 2009, Royal Society of Chemistry
- ItemData-processing technique for the Taipan “Be-filter” neutron spectrometer at the Australian Nuclear Science and Technology Organisation(American Institute of Physics (AIP), 2021-07-09) Iles, GN; Rule, KC; Peterson, VK; Stampfl, APJ; Elcombe, MMThere are five filter-analyzer neutron spectrometers available worldwide for scientists to use in order to measure the vibrational density of states in various samples. While Taipan, the thermal spectrometer, has been operated as a triple-axis spectrometer at the Australian Centre for Neutron Scattering since 2010, a beryllium filter analyzer spectrometer was added in 2016. Due to the complex nature of the data post-processing, it has thus far been impossible to fully treat experimental data from scientific measurements taken over the last five years. We have successfully created a robust method of treating data from the Taipan filter-analyzer and present the method on three different samples. The data-treatment process includes correction for the non-linear energy variation of a particular monochromator, removal of higher-order wavelength contamination, and estimation of low-energy multiple-scattering. The steps described here can be utilized by all users of the Australian Nuclear Science and Technology Organisation “Be-filter”—past, present, and future. © 2021 Author(s). Published under an exclusive license by AIP Publishing.
- ItemDefect perovskites in the SrO-ZrO2-Nb2O5 system(Australian Institute of Physics, 2006-02-07) Schmid, S; Elcombe, MM; Rhode, MCompounds that can reversibly intercalate lithium have the potential to be used as cathodes in rechargeable lithium ion batteries. Two characteristics, the availability of interstitial or defect sites for the incorporation of lithium and the presence of reducible cations are found in some defect perovskites. The aim of this study is to synthesise a number of defect perovskites, which might be useful as host materials for Li intercalation, and investigate their structures using X-ray and neutron powder diffraction. The SrxNbO3, 0.7 ≤ x ≤ 1, solid solution having niobium in both oxidation states +IV and +V whenever x < 1, has been reported to adopt the ideal cubic perovskite structure across the whole solid solution field. Despite intensive searching when data were collected on good quality single crystals no additional reflections were detected [1]. This indicates random ordering between strontium and vacancies on the perovskite A sites. Given the vacancies in the structure (particularly at the low strontium end of the solid solution) and the accompanying presence of niobium +V, which can be easily reduced by lithium metal, this solid solution appeared to be an interesting candidate to investigate Liintercalation properties. Given that niobium +IV is not stable at high temperatures in air but rather gets oxidised, previous syntheses of the solid solution were conducted in high vacuum. Substitution of all niobium +IV by zirconium +IV allows syntheses to be carried out in air. Since previous studies have shown that niobium and zirconium are able to occupy positions in a structure at random [2-4], it was expected that a similar solid solution might be formed. Therefore an investigation was undertaken in the SrO-ZrO2-Nb2O5 system to see whether an analogous solid solution is indeed formed, what the extent of the solid solution range is and whether this material has the potential to intercalate Li ions reversibly.
- ItemDetermination of martensite structures of the Au7Cu5Al4 and Au7Cu5.7Al3.3 shape-memory alloys(Elsevier, 2014-10-15) Elcombe, MM; Kealley, CS; Bhatia, VK; Thorogood, GJ; Carter, DJ; Avdeev, M; Cortie, MBThe β-phase of Au7Cu5Al4 undergoes a reversible shape-memory phase transformation for which several conflicting martensite phases have been reported. Here we show the significance of the cooling temperature used to obtain the martensite. If Au7Cu5Al4 is cooled from the parent phase condition to cryogenic temperatures, e.g. below 200 K, the martensitic phase is orthorhombic (space group Pcmn, a = 4.4841 Å, b = 5.8996 Å, c = 17.8130 Å); however, when this composition is cooled to only ∼260 K it will in general consist of a mixture of orthorhombic and monoclinic phase (the latter has space group P21/m, a = 4.4742 Å, b = 5.9265 Å, c = 13.3370 Å, β = 91.425°). In contrast, a sample with decreased Al content (Au7Cu5.7Al3.3) transforms fully to monoclinic phase if cooled to ∼260 K. © 2014 Acta Materialia Inc.
- ItemDevelopment of carbon nanotube reinforced hydroxyapatite bioceramics(Elsevier B. V., 2005-11-27) Kealley, CS; Elcombe, MM; Ben-Nissan, B; van Riessen, AThis paper reports development of a production method to create a composite material that is biocompatible, which will have high mechanical strength and resilience, and be able to withstand exposure to the physiological environment. The chemical precipitation conditions necessary for the production of single phase synthetic hydroxyapatite (HAp) have been determined. Neutron and X-Ray diffraction have been used extensively to follow the effects of drying and heat treatments on the process and to confirm that the final material is single phase. The neutron diffraction data has enabled the positions of the hydroxide bonds to be determined. Subsequent development of a technique to produce a HAp + carbon nanotube composite material is also reported. A method has been determined to remove the soot impurity from the nanotubes with minimal degradation of the nanotube. Neutron diffraction patterns collected before and after sintering show that the nanotubes have remained in the structure while most of the remaining soot has burnt off. Small angle neutron scattering, in conjunction with transmission electron microscopy, also shows preservation of the carbon nanotubes. Mechanical property testing is in progress and results will be reported. © The Authors
- ItemDevelopment of carbon nanotube-reinforced hydroxyapatite bioceramics(Elsevier B. V., 2006-11-15) Kealley, CS; Elcombe, MM; van Riessen, A; Ben-Nissan, BThis paper reports development of a production method to create a composite material that is biocompatible, which will have high mechanical strength and resilience, and be able to withstand exposure to the physiological environment. The chemical precipitation conditions necessary for the production of single-phase synthetic hydroxyapatite (HAp) and a HAp and carbon nanotube (CNT) composite material have been optimised. Neutron diffraction patterns collected before and after sintering show that the nanotubes have remained intact within the structure, while most of the remaining soot has burnt off. Small-angle neutron scattering, in conjunction with scanning electron microscopy (SEM), also shows preservation of the CNTs. Hot isostatically pressed samples showed excellent densification. Neutron diffraction data has enabled the positions of the hydroxide bonds to be determined, and shown that the addition of the CNTs has had no effect on the structural parameters of the HAp phase, with the exception of a slight reduction in the unit cell parameter α . © 2006 Elsevier B.V.
- ItemDiffuse scattering in the cesium pyrochlore CsTi0.5W1.5O6(Elsevier, 2008-04-01) Thorogood, GJ; Saines, PJ; Kennedy, BJ; Withers, RL; Elcombe, MMThe structure of the defect pyrochlore CsTi0.5W1.5O6 has been investigated using electron, synchrotron X-ray and neutron diffraction methods. The material is cubic a = 10.2773 angstrom with displacive disorder of the Cs cations along the < 1 1 1 > direction. The local structure, revealed by the diffuse structure in the electron diffraction patterns shows there is correlated displacement of the heavy Cs atoms along the < 1 1 0 > directions. The thermal expansion of the material is also described. © 2008, Elsevier Ltd.
- ItemDisordered structures and low temperature dielectric relaxation properties of two misplaced-displacive cubic pyrochlores found in the Bi2O3–MIIO–Nb2O5 (M=Mg, Ni) systems(Elsevier, 2007-09) Nguyen, HB; Norén, L; Liu, Y; Withers, RL; Wei, XY; Elcombe, MMThe disordered structures and low temperature dielectric relaxation properties of Bi1.667Mg0.70Nb1.52O7 (BMN) and Bi1.67Ni0.75Nb1.50O7 (BNN) misplaced-displacive cubic pyrochlores found in the Bi2O3–MIIO–Nb2O5 (M=Mg, Ni) systems are reported. As for other recently reported Bi-pyrochlores, the metal ion vacancies are found to be confined to the pyrochlore A site. The B2O6 octahedral sub-structure is found to be fully occupied and well-ordered. Considerable displacive disorder, however, is found associated with the O' A2 tetrahedral sub-structure in both cases. The A-site ions were displaced from Wyckoff position 16d (1/2, 1/2, 1/2) to 96 h (1/2, 1/2-éA, 1/2 + éA while the O' oxygen was shifted from position 8b (3/8, 3/8, 3/8) to Wyckoff position 32e (3/8 + éọ, 3/8 + éọ, 3/8 + éọ). The refined displacement magnitudes off the 16d and 8b sites for the A and O' sites were 0.408 Å/0.423 Å and 0.350 Å/0.369 Å for BMN/BNN, respectively. © 2007, Elsevier Ltd.
- ItemFracture mechanics of mollusc shells(The Bragg Institute, Australian Nuclear Science and Technology Organisation, 2005-11-27) Cortie, MB; McBean, KE; Elcombe, MMThe shape and structure of the shells of molluscs has attracted considerable attention. One aspect of interest is the comparatively high resistance to fracture of these shells. It is known that they are composite structures of aragonite, other calcereous materials, and up to 5% by volume of protein ‘glue’. A large component of their toughening derives from crack tip blunting, deflection and closure, concepts well-known from the field of fracture mechanics. However, the possibility that they might also derive a measure of toughening from a residual stress distribution has been generally overlooked, although Illert first raised this over a decade ago. The optimum situation would be when the inner surface of the shell is maintained in a state of tensile stress, while the outer layers are in the necessarily counter-balancing compressive state. We have examined this hypothesis using a combination of neutron diffraction and scanning electron microscopy and find that it is certainly feasible. However, a definitive proof will require a diffraction study. © The Authors
- ItemFracture mechanics of mollusc shells(Elsevier B. V., 2006-11-15) Cortie, MB; McBean, KE; Elcombe, MMThe shape and structure of the shells of molluscs has attracted considerable attention. One aspect of interest is the comparatively high resistance to fracture of these shells. It is known that they are composite structures of aragonite, other calcereous materials, and up to 5% by volume of protein ‘glue’. A large component of their toughening derives from crack tip blunting, deflection and closure, concepts well-known from the field of fracture mechanics. However, the possibility that they might also derive a measure of toughening from a residual stress distribution has been generally overlooked, although Illert first raised this over a decade ago. The optimum situation would be when the inner surface of the shell is maintained in a state of tensile stress, while the outer layers are in the necessarily counter-balancing compressive state. We have examined this hypothesis using a combination of neutron diffraction and scanning electron microscopy and find that it is certainly feasible. However, a definitive proof will require a diffraction study at higher resolution. © 2006 Elsevier B.V.
- ItemHigh temperature transformations of the Au7Cu5Al4 shape-memory alloy(Elsevier, 2011-02-24) Cortie, MB; Kealley, CS; Bhatia, VK; Thorogood, GJ; Elcombe, MM; Avdeev, MThe β-phase of Au7Cu5Al4 undergoes a reversible shape-memory phase transformation, however there has been some uncertainty regarding the crystal structure or structures of the parent phase. Here we show that, under equilibrium conditions, the parent phase possesses the L21 structure between its Ap (about 79°C) and 630°C, and the B2 primitive cubic structure between 630°C and its melting point. It melts directly from B2 into the liquid state and hence never achieves the random bcc A2 structure that has been previously mooted. Splat-cast samples of the alloy are martensitic, proving that development of equilibrium order and defect concentration are not pre-requisites for the A → M transformation to occur. © 2011, Elsevier Ltd.
- ItemInelastic neutron scattering from cubic stabilised zirconia(Australian and New Zealand Institutes of Physics, 1994-02-09) Argyriou, DN; Elcombe, MMPhonon dispersion curves have been measured for three cubic stabilised zirconias (CSZ) with varying amounts of oxygen vacancies (Zr(Y)O1.193, Zr(Ca)O1.875, Zr(Y)O1.805), using a triple axis spectrometer. We have been able to observe transverse (TA) and longitudinal acoustic (LA) branches for these crystals. However in agreement with previous work, and despite an exhaustive search in (Q,ω) space, optic modes were not observed 1. The behaviour of the LA and TA branches is atypical, in that phonons become increasingly broader, and weaker close to the Brillouin zone boundary. This is particularly the case for the [ζζ0] direction, where the TA2 branch disappears beyond ζ=0.45. This atypical behaviour has been speculated to be caused by to the defect fluorite structure of CSZ. Recently a reliable model of the static structure has been determined 2 and has been used here to explain the observed inelastic neutron scattering observations. To understand the effect of the defect structure of CSZ to the observed neutron measurements, lattice dynamical calculations have been carried out on the basis of the static structure. These calculations show that the stability of CSZ is particular sensitive to the [100] interactions between oxygen atoms. They show that either relatively small variations in the force constants for this interaction, associated with variations of the 0-0 bondlengths in the defect structure, or the incorporation of vacancies into the structure can render the [(ζζ0] TA2 mode mutable. This is in agreement with the experimental results which shows that this mode disappears rapidly. These calculations also show a general broadening of all phonon branches. This makes the measurer lent of the optic phonon particularly difficult. It is found therefore that the static defect model of CSZ is consistent with the inelastic neutron scattering measurements.
- ItemInsights into Li ion batteries using in-situ neutron powder diffraction(Society for Chemical Engineering and Biotechnology (DECHEMA), 2010-06-01) Sharma, N; Peterson, VK; Elcombe, MM; Avdeev, M; Studer, AJ; Kamarulzaman, NWe apply in-situ neutron diffraction to investigate charge/discharge processes in a commercially available rechargeable lithium ion battery, LiCoO{sub 2}/C. Phase transformations are observed in both layered LiCoO{sub 2} and spinel-type LiCoO{sub 2} as Li is removed and re-inserted during electrochemical cycling. Similarly, the graphite anode exhibits behaviour in accordance with Li insertion/extraction.
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