Brendan J. Kennedy's research while affiliated with The University of Sydney and other places

Publications (382)

Article
The crystal structure of potassium μ-oxo-bis[pentabromoruthenate] K4Ru2OBr10, determined from synchrotron X-ray powder diffraction, is described. Each Ru atom is surrounded by five Br atoms and one O atom. Magnetic measurements show the complex to be diamagnetic as a result of strong Ru–Ru interactions facilitated by the linear Ru–O–Ru linkage.
Article
Titanium dioxide (TiO2) photocatalyst is widely used in wastewater treatment. The favourable attributes of TiO2 such as chemically stability, cost-effectiveness, low toxicity to humans and high catalytic activity have received extensive attention from researchers seeking to design better materials. Nevertheless, one of the drawbacks of TiO2 photoca...
Article
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Various layered lead halide perovskites based on the Ruddlesden–Popper (RP) structure with the general formula of An+1BnX3n+1 (n = 1, 2, …) have been developed. Most of them are comprised of alternating layered perovskite-like stacks and an organic spacer with a long insulating chain especially for the A-site-substituted RP-type perovskites. To dat...
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2D Perovskites Cs2Pb(SCN)2Br2, an inorganic‐cation pseudo‐halide 2D phase perovskite single crystal, is grown by a simple antisolvent vapor‐assisted crystallization method, as reported by Chu‐Chen Chueh, Anita W. Y. Ho‐Baillie, and co‐workers in article number 2104782. Cs2Pb(SCN)2Br2 exhibits a reversible first‐order phase transformation to CsPbBr2...
Article
Phase transition and high-temperature properties of NdNbO4 and NdTaO4 were studied in situ using powder neutron diffraction methods. Both oxides undergo a reversible phase transition from a monoclinic I2/a phase at low temperatures to a tetragonal I41/a phase at high temperatures. The phase transition has been investigated through analysis of the s...
Article
We have synthesized polycrystalline and single crystal samples of Sr4Nb2O9 and Sr5Nb2O10 and revisited the crystal structure of the high-temperature cubic phase. By careful analysis of single-crystal X-ray diffraction (SXRD), powder synchrotron X-ray diffraction (Syn-PXRD) and powder neutron diffraction (PND) data, we arrive at a structure model in...
Article
The chemical speciation of uranium oxides is sensitive to the provenance of the samples and their storage conditions. Here, we use diffraction methods to characterize the phases found in three aged (>10 years) uranium ore concentrates of different origins as well as in situ analysis of the thermally induced structural transitions of these materials...
Article
The long-range (average) and short-range (local) structures in the Yb2(Ti2-xYbx)O7-x/2 (x = 0.00–0.67) series were studied using a combination of diffraction and spectroscopic techniques. The average structure, established from synchrotron X-ray and neutron powder diffraction data, shows the development of multiphase regions from x = 0.134 and the...
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The structure of lead-technetium pyrochlore has been refined in space group F d 3 ¯ m with a = 10.36584(2) Å using a combination of synchrotron X-ray and neutron powder diffraction data and confirmed via Electron Diffraction. The oxide is found to be oxygen deficient with a stoichiometry of Pb2Tc2O7-d. Displacive disorder of the Pb cations is evide...
Article
The impact of Ta doping on two orthoniobates SmNbO4 and HoNbO4 has been studied using a combination of high-resolution powder diffraction and Density-Functional Theory calculations. In both ANb1-xTaxO4 (A = Sm, Ho) series the unit cell volume decreases as the Ta content increased demonstrating that the effective ionic radii of Ta is smaller than th...
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Photocatalytic degradation by the titanium dioxide (TiO2) photocatalyst attracts tremendous interest due to its promising strategy to eliminate pollutants from wastewater. The floating photocatalysts are explored as potential candidates for practical wastewater treatment applications that could overcome the drawbacks posed by the suspended TiO2 pho...
Article
The long-range average and short-range local structures in the Tm2(Ti2-xTm x )O7-x/2 (x = 0.00-0.67) series were studied using a combination of diffraction and spectroscopic techniques. The long-range average structure, established from synchrotron X-ray and neutron powder diffraction data, shows the development of multiphase regions from x = 0.134...
Article
A systematic investigation examining the origins of structural distortions in rutile-related ternary uranium AUO4 oxides using a combination of high-resolution structural and spectroscopic measurements supported by ab initio calculations is presented. The structures of β-CdUO4, MnUO4, CoUO4, and MgUO4 are determined at high precision by using a com...
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Transport properties of perovskite-type Sr11Mo4O23 and composite Sr11Mo4O23 - 1 wt% Al2O3 were studied at 400–1300 K in the oxygen partial pressure range from 0.21 down to 10−19 atm. The electromotive force and faradaic efficiency measurements, in combination with the energy-dispersive spectroscopy of the fractured electrochemical cells, unambiguou...
Article
Na2O2 is one of the possible discharge products from sodium-air batteries. Here, we report the evolution of the structure of Na2O2 from room temperature to 500 °C using variable-temperature neutron and synchrotron X-ray powder diffraction. A phase transition from α-Na2O2 to β-Na2O2 is observed in the neutron diffraction measurements above 400 °C, a...
Article
The present work describes a density-functional theory (DFT) study of TlReO4 in combination with powder x-ray diffraction experiments as a function of temperature and Raman measurements at ambient temperature. X-ray diffraction measurements reveal three different structures as a function of temperature. A monoclinic structure (space group P21/c) is...
Article
The impact of Li doping on the temperature-induced phase transitions in silver niobates Ag1-xLi x NbO3 has been investigated using a combination of high-resolution powder neutron diffraction and synchrotron X-ray diffraction. Considering both the cell metric and distortions of the NbO6 octahedra, estimated by Rietveld refinements, it is shown that...
Article
The synthesis, structures and magnetism of six mixed 3d-5d oxides Ba3BM2O9 (B = Ti, Y, Zn; M = Ru, Os) are described. When prepared at ambient pressure the six oxides display a 6H type perovskite structure comprised of corner sharing BO6 and face sharing M2O9 motifs. Synchrotron X-ray diffraction reveals a small monoclinic distortion in Ba3ZnRu2O9;...
Article
Acetonitrile has been observed within the atmosphere of Titan, Saturn’s largest moon, and as a result it is assumed that it will be a significant surface solid (mineral) upon Titan. Solid acetonitrile is known to adopt high-temperature (α) and low temperature forms (β) with the β form assumed to be the stable phase under Titan surface conditions. W...
Cover Page
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Cover illustration: Doping is an effective way to modify structural and electronic properties of inorganic compounds, especially perovskite oxides, and the selective site-doping may tune the material functionalities. The selectivity of Eu2+/Eu3+-doping at Sr2+- and Sn4+-sites in SrSnO3 compounds is reported, and the combination of experimental anal...
Article
Supporting Information, ACS Publications. Journal contribution. Experimental section: synthesis, material characterization, photocatalytic experiments, ecotoxicity analysis, and theoretical methods (DFT simulations); results: refined structural parameters, IR and Raman spectroscopy data, XPS and XANES spectra, electronic defects evaluation by PL...
Article
Eleven members of the series Tb2Sn2-xZrxO7 were synthesized and characterized by a combination of Synchrotron X-ray diffraction and Raman spectroscopy. S-XRD shows that Tb2Sn2O7 has a pyrochlore structure, and Tb0.5Zr0.5O2-x has a defect fluorite structure. Both techniques demonstrate that the addition of Zr⁴⁺, which reduces the ratio of the averag...
Article
The impact of Eu3+ doping at the Sr2+ and Sn4+ sites in SrSnO3 on its structural and electronic properties was studied and correlated with the photocatalytic efficiency. The compounds were synthesized using a modified Pechini method. Refinement of the synchrotron X-ray diffraction (S-XRD) data showed that the samples had an orthorhombic Pbnm symmet...
Article
The double perovskite Ba2CoOsO6, synthesized using solid-state methods at ambient pressure, is shown as a rare example of an oxide adopting the 6L-trigonal (S.G.: P3̅m1) perovskite structure. The structure, refined using a combination of X-ray and neutron diffraction data, showed the Co and Os were ordered over the two dimer sites with additional o...
Article
The structure and magnetic properties of the mixed technetium-ruthenium perovskites SrTcxRu1-xO3 (x = 0.25 and 0.5) have been investigated using variable temperature synchrotron X-ray diffraction, magnetic susceptibility measurements, and DFT calculations. Both oxides are isostructural with SrRuO3 and SrTcO3, and there is no evidence of long-range...
Article
Two polymorphs of lithium magnesium tellurate Li4–2xMg1+xTeO6 have been prepared by solid-state reactions and their crystal structures characterised by powder X-ray and neutron diffraction. For x ≈ 0, a monoclinic C2/m phase is obtained, structurally similar to other O3 type honeycomb layered tellurate and antimonate compounds. The basic structure...
Article
Oxides of the form ABO4 with A = K, Rb, Cs and B = Ru and Os have been synthesized and characterized by diffraction and magnetic techniques. For A = K the oxides adopted the tetragonal (I41/a) scheelite structure. RbOsO4, which crystallizes as a scheelite at room temperature, underwent a continuous phase transition to I41/amd near 550 K. RbRuO4 and...
Article
The structures of the six perrhenates (AReO4 A = Ag, Na, K, Rb, Cs and Tl) at room temperature have been established using powder neutron diffraction methods. These demonstrate the rigid nature of the ReO4 tetrahedra, with the Re-O distances decreasing very slightly and the O-Re-O bond angles approaching the regular tetrahedron value of 109.5⁰ as t...
Article
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Li3Co2SbO6 is found to adopt two highly distinct structural forms: a pseudohexagonal (monoclinic C2/m) layered O3-LiCoO2 type phase with "honeycomb" 2:1 ordering of Co and Sb, and an orthorhombic Fddd phase, isostructural with Li3Co2TaO6 but with the addition of significant Li/Co ordering. Pure samples of both phases can be obtained by conventional...
Article
Synchrotron X-ray powder diffraction methods have been used to obtain accurate structures of the lanthanoid orthoniobates, LnNbO4 at room temperature. The observed decrease in the unit cell volume in going from Ln = La to Lu correlates with a decrease in the volume of the LnO8 polyhedra due to the changing size of the Ln³⁺ cation. In all cases the...
Article
The temperature dependence of the structures of four pertechnetates (ATcO4A = Ag, Tl, Rb, Cs) from 90 K to their melting points is described. Synchrotron X-ray diffraction measurements show that RbTcO4 undergoes a I41/a to I41/amd transition near 530 K that is associated with a change in the orientation of the TcO4- tetrahedra about the scheelite b...
Preprint
div>Li3Co2SbO6 is found to adopt two highly distinct structural forms: a hexagonal layered O3- LiCoO2 type phase with “honeycomb” 2:1 ordering of Co and Sb; and an orthorhombic superstructure of rock-salt type, isostructural with Li3Co2TaO6 but with the addition of significant Li/Co ordering. Pure samples of both phase scan be obtained by conventio...
Article
The synthesis of polycrystalline samples of B-site doped SrRu1-xMxO3 with x ≤0.2 by solid state methods is described for a number of dopants M = Mg, Mn, Fe, Co, Ni, Cu, or Zn) and the structures of these established using Synchrotron X-ray powder diffraction, and for SrRu0.8Cu0.2O3 high resolution neutron diffraction. With the exception of M = Cu,...
Article
The quantum magnet KOsO4 has been characterized by a combination of X-ray and neutron diffraction techniques. The tetrahedrally coordinated Os7+ 5d1 S = ½ cations were determined to order antiferromagnetically...
Article
Having identified a set of conditions that predispose a solid-state ionic compound to a pressure-induced valence transition, we investigated a series of bismuth(III) perovskite oxides. We found such a transition...
Article
The thermal expansion of NH 4 TcO 4 and NH 4 ReO 4 between 97 and 500 K has been established using variable temperature synchrotron X-ray diffraction. Both oxides display a tetragonal scheelite-type structure over the temperature range. The observed anomalous thermal expansion is associated with disorder in the orientation of the NH 4 groups and th...
Article
Oxides of the type SrTi1-xSnxO3 have been prepared using both a solid state and polymeric precursor method and characterized using high-resolution Synchrotron X-ray Diffraction and X-ray Absorption and Raman spectroscopies. The diffraction measurements demonstrate that a continuous pseudo-solid solution exists between the cubic SrTiO3 and orthorhom...
Article
High resolution synchrotron X-ray powder diffraction (S-XRD) methods have been used to study the temperature dependence of the structure of β-MnO2 between room temperature and 400 °C. Rietveld analysis of the S-XRD data provided accurate and precise until cell parameters from which the thermal expansion coefficients (TEC) were determined, αa = 7.8...
Article
In situ synchrotron powder X-ray diffraction measurements have demonstrated that SrUO4 undergoes a reversible phase transformation under reducing conditions at high temperatures, associated with the ordering of oxygen defects resulting in a lowering of crystallographic symmetry. When substoichiometric rhombohedral α-SrUO4- x, in space group R3̅ m w...
Article
The series of ruthenate double perovskites Ba2-xSrxHoRuO6 (0 ≤ x ≤ 2) have been synthesized using solid state methods. The crystal structures of the series have been determined by high resolution synchrotron X-ray diffraction and show the sequence of structures to be Fm3̅m (a⁰a⁰a⁰) (0 ≤ x ≤ 0.6) → I4/m (a⁰a⁰c⁻) (x = 0.8) → I2/m (a⁰b⁻b⁻) (1.0 ≤ x ≤...
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Refinement of time-of-flight high-resolution neutron powder diffraction data for lueshite (Na, Ca)(Nb, Ta, Ti)O3, the natural analogue of synthetic NaNbO3, demonstrates that lueshite at room temperature (298 K) adopts an orthorhombic structure with a 2ap × 2ap × 4ap superlattice described by space group Pmmn [#59: a = 7.8032(4) Å; b = 7.8193(4) Å;...
Article
The paraelectric-ferroelectric transition in CdTiO3 has been monitored using high-resolution neutron diffraction data. This necessitated preparing a sample enriched in Cd114. A subtle, but significant, anisotropy in the thermal expansion of the lattice parameters for CdTiO3 associated with the transition to the polar structure was observed. First-p...
Article
Polycrystalline Nd2MgRuO6 has monoclinic P21/n structure with an ordered arrangement of Mg²⁺ and Ru⁴⁺ ions. Magnetic ordering is observed at 1.5 K where the Ru sublattice exhibits type-I antiferromagnetic order with the magnetic moments parallel to the c-axis. The Nd³⁺ cations show a ferromagnetic arrangement at this temperature. Nd2MgRuO6 exhibits...
Article
The long range average crystal structure as well as the short and medium range structural features of the A-site deficient and oxygen deficient perovskite Sr11Mo4O23 have been determined. Rietveld refinement of synchrotron X-ray and neutron powder diffraction data show that this compound is cubic with space group Fd-3m and a lattice parameter of a...
Article
The structure of BaThO3, obtained by solid state synthesis, was refined for the first time by the Rietveld method using a combination of synchrotron X-ray and neutron powder diffraction data. BaThO3 has an orthorhombic structure at room temperature, in space group Pbnm with a = 6.3491(5), b = 6.3796(4) and c = 8.9907(7) Å. Heating BaThO3 to above 7...
Article
TcO2 has a monoclinic structure in space group P21/c between 25 and 1000 °C, as established using a combination of synchrotron X-ray and neutron powder diffraction methods, and is found to remain monoclinic in the same space group. Thermal expansion of the lattice is highly anisotropic, with negative thermal expansion of the b axis observed above 7...
Article
The synthesis, structural, and magnetic properties of some ruthenium-containing double perovskites A2ScRuO6 are described. The ambient-pressure hexagonal and high-pressure cubic polymorphs of Ba2ScRuO6 exhibit different magnetic and electronic properties: cubic Ba2ScRuO6 displays a metal−insulator transition near 270 K, and hexagonal Ba2ScRuO6 is a...
Cover Page
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Cover illustration: Anion ordering of ATaO2N (bottom left: BaTaO2N; top right: SrTaO2N) from ideal disordered perovskite (top left) and with tilting of the octahedra in SrTaO2N (bottom right) [see Wang et al. (2017). Acta Cryst. B73, 389-398].
Article
In this work we synthesized BaTaO 2 N and SrTaO 2 N using a two-step high-temperature solid-state reaction method and analysed the structural distortions, relative to the ideal cubic perovskite structure, according to group theory. From a complete distortion analysis/refinement using high-resolution neutron diffraction data in the temperature range...
Article
The crystal and magnetic structures of double perovskites of the type Ba2-xSrxYOsO6 were studied by synchrotron X-ray and neutron powder diffraction methods, bulk magnetic susceptibility measurements, and X-ray absorption spectroscopy. The structures were refined using combined neutron and synchrotron data sets based on an ordered array of corner-s...
Article
Full-text available
The ferroelectric–paraelectric transition in Li0.2Na0.8NbO3 is between two extremely rare perovskite polytypes. How the unprecedented sequence of structures was established shows that even old oxides can play new tricks.
Article
The impact of chemical doping of the type Sr2-xAxYRuO6 (A = Ca, Ba) on the low temperature magnetic properties of Sr2YRuO6, probed using variable temperature magnetic susceptibility, neutron diffraction and heat capacity measurements, are described. Specific-heat measurements of un-doped Sr2YRuO6 reveal two features at ∼ 26 and ∼30 K. Neutron scatt...
Article
The Sr1−xBaxTcO3 (x=0, 0.1, 0.2) oxides were prepared and their solid-state and magnetic structure studied as a function of temperature by x-ray and neutron powder diffraction. The refined Tc moments at room temperature and Néel temperatures for Ba0.1Sr0.9TcO3 and Ba0.2Sr0.8TcO3 were 2.32(14)μβ and 2.11(13)μβ and 714∘C and 702∘C, respectively. In c...
Article
The temperature dependence of the structures of three polytypes of BaRuO3 have been investigated between room temperature and 1000 °C using high resolution Synchrotron X-ray diffraction. The structural studies reveal a systematic decrease in the Ru-Ru distance as the pressure required to prepare the polytype increases. The O-O distance across the s...
Article
The structural and magnetic properties of the two Ir(V) perovskites Ba2ScIrO6 and Sr2ScIrO6 were established. The structures were refined using a combined neutron and synchrotron data set. At room temperature the former has a cubic structure in space group Fm3̅m with a = 8.1450(3) Å, and the latter is monoclinic in P21/n with a = 5.6606(3) Å, b = 5...
Article
We have studied the long-range average and short-range local structures in Y2Ti2-xHfxO7 (x = 0-2.0) using diffraction and spectroscopy techniques respectively. Both neutron and synchrotron X-ray powder diffraction data show a clear phase transition of the average structure from ordered pyrochlore to disordered defect-fluorite at x ~ 1.6; the long-r...
Article
Four novel alkaline earth metal uranyl borates, namely, A[(UO2)5(BO3)2O2(OH)2]∙5H2O (SrUBO-1, BaUBO-1) and A[(UO2)2(B2O5)O] (SrUBO-2, BaUBO-2) (A = Sr, Ba), have been prepared. SrUBO-1, BaUBO-1, and BaUBO-2 were synthesized using hydrothermal methods, whereas SrUBO-2 was prepared by a traditional high-temperature solid-state method. The compounds S...
Article
Polycrystalline gaudefroyite-type YCa3(CrO)3(BO3)4 with Cr3+ ions (3d3, S = 3/2) forming an undistorted Kagome lattice is prepared by reaction of a stoichiometric mixture of Y2O3, CaCO3, Cr2O3, H3BO3 in a KCl flux (Al2O3 crucible, 1000 °C, 1 d) followed by re-grinding and further annealing (1000 °C, 2 d, 95% yield).
Article
In situ neutron and synchrotron X-ray diffraction studies demonstrate that SrUO4 acts as an oxygen transfer agent, forming oxygen vacancies under both oxidizing and reducing conditions. Two polymorphs of SrUO4 are stable at room temperature, and the transformation between these is observed to be associated with thermally regulated diffusion of oxyg...
Article
We report the occurrence of a magnetodielectric effect and its correlation with structure and magnetism in the A-site ordered chromate spinel oxides LiMCr4O8 (M=Ga, In). In addition to magnetic and dielectric measurements, temperature dependent synchrotron and neutron diffraction experiments have been carried out for the Ga compound. The results ar...
Article
We report a new gaudefroyite-type compound YCa3(CrO)3(BO3)4, in which Cr(3+) ions (3d(3), S = 3/2) form an undistorted kagomé lattice. Using a flux agent, the synthesis was significantly accelerated with the typical calcining time reduced from more than 2 weeks to 2 d. The structure of YCa3(CrO)3(BO3)4 was determined by combined Rietveld refinement...
Article
A combination of S-XRD and NPD demonstrate the structure of Ba2Y0.879UO6+x to be monoclinic in space group I2/m. That the U is hexavalent is evident from the U L2-edge XANES measurements. This appears to be a rare example of a double perovskite containing vacancies at the octahedral B-sites and interstitial oxygen defects, which combine to stabilis...
Article
The hexagonal perovskites Ba3BiIr2O9, Ba3BiRu2O9, and Ba4BiIr3O12 all undergo pressure-induced 1% volume collapses above 5 GPa. These first-order transitions have been ascribed to internal transfer of valence electrons between bismuth and iridium/ruthenium, which is driven by external applied pressure because the reduction in volume achieved by emp...
Article
Polycrystalline SrOsO3 is prepared by hot-press sintering and investigated using powder neutron diffraction at 5—300 K and powder synchrotron XRD at 80—870 K.
Article
Temperature dependent high resolution neutron diffraction studies demonstrate that the sequence and temperatures of the crystallographic phase transitions in NaTaO3 are not impacted by doping with 1% K to form Na0.99K0.01TaO3. Rietveld analysis of the neutron diffraction data shows the structural transitions to be: Pbnm↔723KCmcm↔803KP4/nbm↔893KPm3¯...
Article
The structures of some AUO4 (A=Ca, Sr, or Ba) oxides have been determined using a combination of neutron and synchrotron X-ray diffraction, supported by X-ray absorption spectroscopic measurements at the U L3-edge. The smaller Ca cation favours a rhombohedral AUO4 structure with 8-coordinate UO8 moieties whilst an orthorhombic structure based on UO...