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We report the synthesis, structure, and redox behavior of the cation-ordered tetragonal Sc2VO5+δ defect fluorite superstructure previously thought to be the oxygen precise A3+2B4+O5 phase. Four synthesis routes in oxidative, reductive, and inert atmospheres are demonstrated. Ex situ and in situ powder X-ray and neutron diffraction analyses reveal vanadium disproportionation reactions. The structure-reaction map illustrates the oxygen-dependent competition between the tetragonal cation and anion ordered Sc2VO5+δ and the disordered cubic Sc2VO5+δ' (δ < δ' ≤ 0.5) phases as a function of temperature. Oxidation states and oxide stoichiometries were determined with DC magnetometry and XANES experiments. The tetragonal cation ordered Sc2VO5+δ phase with δ = -0.15(2) for as-synthesized samples reveals vanadium charge ordering. V3+ and V4+ cations occupy octahedral sites, whereas V5+ predominantly occupies a tetrahedral site. The paramagnetic 8g{V3+/4+}4 clusters are isolated by diamagnetic 2cV5+ cations. At temperatures below 500 °C the 8g{V3+/4+}4 clusters can be topotactically fine-tuned with varying V3+/V4+ ratios. Above 600 °C the tetragonal structure oxidizes to the cubic Sc2VO5+δ' fluorite phase-its disordered competitor. The investigation of the cation- and anion-ordered Sc-V-O phases, their formation, and thermal stability is important for the design of low-temperature solid state oxide ion conductors and vacancy structures.

SrLaMnO4 is a layered antiferromagnetic (AF) oxide with the tetragonal ( I4/ mmm) n = 1 Ruddlesden-Popper phase structure (also known as the K2NiF4 structure) with TN = 128 K. Remarkably, substitution of Sr2+ by Ba2+, forming the solid solution Ba1- xSr xLaMnO4, results in the destruction of long-range magnetic order and of the ordered moment on Mn3+ for x > 0.35, although the effective paramagnetic moment remains unchanged, an unprecedented behavior for this class of magnetic materials. Four members, x = 0.0, 0.25, 0.35, and 1.0, have been studied using XYZ neutron polarization analysis which permits isolation of the magnetic, nuclear and nuclear spin components of the scattering and the measurement of the absolute value of the magnetic cross section. Data analysis is done using model independent reverse Monte Carlo methods (SPINVERT). The results for x = 0.0 (SrLaMnO4), T > TN(128 K), show an asymmetric diffuse peak which evolves into resolution limited Bragg peaks below T N and a fully ordered AF ground state with a Mn3+ moment of 3.06 μB. For x = 0.25 the magnetic scattering below T N displays a remarkable phase separation-Bragg reflections coexisting with diffuse scattering. The ordered Mn3+ moment is 1.1 μB, much reduced from that obtained via unpolarized neutrons. There are no Bragg peaks for x = 0.35 at any measured temperature ( T > 3 K) but there is highly structured diffuse scattering indicating strong short-range order reminiscent of x = 0 and 0.25 above their respective transition temperatures. For x = 1.00 (BaLaMnO4) the diffuse scattering roughly follows a paramagnetic form-factor indicating no short or long-range magnetic correlations. It is argued that the observed phenomena are due to a competition between AF and ferromagnetic (F) superexchange interactions for the 180° Mn3+-O-Mn3+ geometry within the ab plane and that the changes in the local geometry of the Mn-O octahedron leads to reduction of the AF interaction with a likely enhancement of the F interaction with increasing Ba content, ultimately giving rise to a glassy ground state. Analysis of the diffuse magnetic components show clear 2D AF spin correlations above TN for x = 0.00, 0.25, and 0.35 with correlation lengths, ξ ∼ 14-7 A and no spin correlations for x = 1.00.

We report, for the first time, members of the Y xPr2- xO3 system with non-bixbyite or defect fluorite structures. The synthesis, structure, phase transitions, and high temperature reactivity of the trigonal A-type and monoclinic B-type structures are reported along with those of the cubic C-type phase (bixbyite). Combined powder X-ray and neutron diffraction Rietveld refinements are used to report structural details of all three reported phases. Phase transitions are investigated, showing a clear dependence on average cation size. Using neutron diffraction, phase transitions are followed in situ, revealing that all high temperature phases are quenchable. In-situ powder X-ray diffraction experiments in flowing oxygen allow insights into mechanistic details of redox processes in the reported phases. In contrast to the C-type cubic bixbyite, the trigonal A-type and monoclinic B-type structures do not allow for topotactic oxygen uptake, displaying instead a phase transition to either the bixbyite C-type capable of accommodating additional oxide anions or the direct oxidation to the cubic defect fluorite structure. The findings reported here agree with the accepted lanthanide sesquioxide phase diagrams and provide exceptional control of phases. The work is important for the prediction of structures, and the synthetic control needed for rational design of functional materials.

Solid oxide fuel cells (SOFCs) are solid-state electrochemical devices that directly convert chemical energy of fuels into electricity with high efficiency. Because of their fuel flexibility, low e...

A few thallium based layered chalcogenides of α-NaFeO2 structure-type are known for their excellent thermoelectric properties and interesting topological insulator nature. TlScQ2 belongs to this structural category. In the present work, we have studied the electronic structure, electrical and thermal transport properties and thermal stability of the title compounds within the temperature range 2–600 K. Density functional theory (DFT) predicts a metallic nature for TlScTe2 and a semiconducting nature for TlScSe2. DFT calculations also show significant lowering of energies of frontier bands upon inclusion of spin–orbit coupling contribution in the calculation. The electronic structure also shows the simultaneous occurrence of holes and electron pockets for the telluride. Experiments reveal that the telluride shows a semi-metallic behaviour whereas the selenide is a semiconductor. The thermoelectric properties for both the materials were also investigated. Both these materials possess very low thermal conductivity which is an attractive feature for thermoelectrics. However, they lack thermal stability and decompose upon warming above room temperature, as evidenced from high temperature powder X-ray diffraction and thermal analysis.

The reduction and oxidation of the solid solution Y2−xPrxO3+δ (0.0≤x ( I a 3 ¯ ) . The oxidized solid solution Y2−xPrxO3+δ (0.0≤x ( I a 3 ¯ ) whereas Y2−xPrxO3+δ (1.4≤x ( F m 3 ¯ m ) with variable oxide defect concentrations. The two cation positions are investigated in detail using synchrotron powder X-ray and time of flight neutron diffraction data. In the bixbyite structures the 8c cation site splits into the 16c cation site and the 24d cation position migrates toward the ideal fluorite coordination upon oxidation. Reductive in-situ diffraction experiments reveal the co-existence of the fluorite and bixbyite structure only in a narrow temperature range. During oxidation of the bixbyite phase a new 16c oxide anion site is populated. The impact of the 16c oxide site population on the cation sublattice is being discussed.

We report novel details regarding the reactivity and mechanism of the solid-state topotactic reduction of Sr2MnO4 using a series of solid-state metal hydrides. Comprehensive details describing the active reducing species are reported and comments on the reductive mechanism are provided, where it is shown that more than one electron is being donated by H(-). Commonly used solid-state hydrides LiH, NaH, and CaH2, were characterized in terms of reducing power. In addition the unexplored solid-state hydrides MgH2, SrH2, and BaH2 are evaluated as potential solid-state reductants and characterized in terms of their reductive reactivities. These 6 group I and II metal hydrides show the following trend in terms of reactivity: MgH2SrH2LiH ≈ CaH2 ≈ BaH2NaH. The order of the reductants are discussed in terms of metal electronegativity and bond strengths. NaH and the novel use of SrH2 allowed for targeted synthesis of reduced Sr2MnO(4-x) (0 ≤ x ≤ 0.37) phases. The enhanced control during synthesis demonstrated by this soft chemistry approach has allowed for a more comprehensive and systematic evaluation of Sr2MnO(4-x) phases than previously reported phases prepared by high temperature methods. Sr2MnO3.63(1) has for the first time been shown to be monoclinic by powder X-ray diffraction and the oxidative monoclinic to tetragonal transition occurs at 450 °C.

We report the formation, structures, temperature-dependent phase transitions, and high-temperature reactivity of the potential proton and oxide ion conductors BaCe(1-x)M(x)O3 (M(3+) = In(3+), La(3+)). The present in situ diffraction studies show oxidative platinum uptake at temperatures as low as 950 °C into BaCeO3, forming the cubic Ba2CePtO6 double perovskite. The transient B-site double perovskite expels platinum at around 1200-1250 °C. Platinum oxidation via BaCeO3 is investigated by in situ powder X-ray and neutron diffraction experiments in various atmospheres. Doped BaCe(1-x)M(x)O3 phases show the formation of Ba2CePtO6 without incorporating the M(3+) dopant. Oxidative platinum uptake is also observed during the synthesis of BaCeO3 on platinum metal. We report the reaction pathway for the low-temperature oxidative formation of Ba2CePtO6 and the subsequent liberation of platinum for the barium cerate system. The findings are supported by ambient-temperature X-ray diffraction, in situ powder X-ray, and powder neutron diffraction as well as XPS.

A systematic study of the atomic position modulation in polycrystalline CaMn 7 O 12 with different particle sizes (determined from scanning electron microscopy) and crystallite sizes (determined from X-ray diffraction) is reported. The morphology and phase composition are characterised by scanning electron microscopy, selected area electron diffraction and energy dispersive X-ray spectroscopy. The crystal structure and the atomic position modulation in polycrystalline CaMn 7 O 12 samples are explored with high-resolution synchrotron radiation based powder X-ray diffraction. The modulation vector and the modulation amplitudes observed at T =10 K do not change as a function of particle size, crystallite size and microstrain fluctuations. In addition, we report and discuss the formation of the additional CaMn 4 O 8 nanowire phase during high temperature annealing.

The novel oxide defect fluorite phase ScTiO(3.5) is formed during the topotactic oxidation of ScTiO(3) bixbyite. We report the oxidation pathway of ScTiO(3) and structure evolution of ScTiO(3.5), Sc(4)Ti(3)O(12), and related scandium-deficient phases as well as high-temperature phase transitions between room temperature and 1300 °Cusing in-situ X-ray diffraction. We provide the first detailed powder neutron diffraction study for ScTiO(3). ScTiO(3) crystallizes in the cubic bixbyite structure in space group Ia3 (206) with a = 9.7099(4) Å. The topotactic oxidation product ScTiO(3.5) crystallizes in an oxide defect fluorite structure in space group Fm3m (225) with a = 4.89199(5) Å. Thermogravimetric and differential thermal analysis experiments combined with in-situ X-ray powder diffraction studies illustrate a complex sequence of a topotactic oxidation pathway, phase segregation, and ion ordering at high temperatures. The optimized bulk synthesis for phase pure ScTiO(3.5) is presented. In contrast to the vanadium-based defect fluorite phases AVO(3.5+x) (A = Sc, In) the novel titanium analogue ScTiO(3.5) is stable over a wide temperature range. Above 950 °C ScTiO(3.5) undergoes decomposition with the final products being Sc(4)Ti(3)O(12) and TiO(2). Simultaneous Rietveld refinements against powder X-ray and neutron diffraction data showed that Sc(4)Ti(3)O(12) also exists in the defect fluorite structure in space group Fm3m (225) with a = 4.90077(4) Å. Sc(4)Ti(3)O(12) undergoes partial reduction in CO/Ar atmosphere to form Sc(4)Ti(3)O(11.69(2)).

We report the first in-situ powder X-ray diffraction (PXRD) study of the BaCO(3)-CeO(2)-In(2)O(3) and CeO(2)-In(2)O(3) systems in air over a wide range of temperature between 25 and 1200 degrees C. Herein, we are investigating the formation pathway and chemical stability of perovskite-type BaCe(1-x)In(x)O(3-delta) (x = 0.1, 0.2, and 0.3) and corresponding fluorite-type Ce(1-x)In(x)O(2-delta) phases. The potential direct solid state reaction between CeO(2) and In(2)O(3) for the formation of indium-doped fluorite-type phase is not observed even up to 1200 degrees C in air. The formation of the BaCe(1-x)In(x)O(3-delta) perovskite structures was investigated and rationalized using in-situ PXRD. Furthermore the decomposition of the indium-doped perovskites in CO(2) is followed using high temperature diffraction and provides insights into the reaction pathway as well as the thermal stability of the Ce(1-x)In(x)O(3-delta) system. In CO(2) flow, BaCe(1-x)In(x)O(3-delta) decomposes above T = 600 degrees C into BaCO(3) and Ce(1-x)In(x)O(2-delta). Furthermore, for the first time, the in-situ PXRD confirmed that Ce(1-x)In(x)O(2-delta) decomposes above 800 degrees C and supported the previously claimed metastability. The maximum In-doping level for CeO(2) has been determined using PXRD. The lattice constant of the fluorite-type structure Ce(1-x)In(x)O(2-delta) follows the Shannon ionic radii trend, and crystalline domain sizes were found to be dependent on indium concentration.

The solid-state structure of (CH3)3SnF was reinvestigated by X-ray diffraction techniques as well as by multi-nuclear solid-state NMR spectroscopy. Trimethyltin fluoride crystallizes from hot ethanol in the orthorhombic space group Pnma at room temperature and changes to a low-temperature orthorhombic phase (space group: Cmcm) below -70 °C. In both modifications, trimethyltin fluoride adopts a linear chain structure with symmetric fluorine bridges, in contrast to previous reports. During its synthesis, (CH3)3SnF precipitates in another, poorly crystalline modification, as shown by powder X-ray diffraction. Solid-state MAS NMR experiments of both room-temperature phases of (CH3)3SnF (non-recrystallized and recrystallized) were carried out for the (1)H, (13)C, (19)F, and (119)Sn nuclei. The (119)Sn{(19)F, (1)H} and (19)F{(1)H} NMR spectra offer unambiguous determination for the (19)F and (119)Sn shielding tensors. The (119)Sn{(1)H} solid-state NMR spectra are in agreement with pentacoordination of Sn in this compound for the non-recrystallized and the recrystallized modifications. Based on the solid-state NMR results, the non-recrystallized modification of (CH3)3SnF also consists of linear, symmetrically fluorine-bridged chains, and differs from the recrystallized orthorhombic phase only in packing of the chains.

We report the first synthesis and high-temperature in situ X-ray diffraction study of InVO3. Polycrystalline InVO3 has been prepared via reduction of InVO4 using a carbon monoxide/carbon dioxide buffer gas. InVO3 crystallizes in the bixbyite structure in space group Ia−3 (206) with a=9.80636(31) A with In3+/V3+ disorder on the (8b) and (24d) cation sites. In situ powder X-ray diffraction experiments and thermal gravimetric analysis in a CO/CO2 buffer gas revealed the existence of the metastable phase InVO3. Bulk samples with 98.5(2)% purity were prepared using low-temperature reduction methods. The preparative methods limited the crystallinity of this new phase to approximately 225(50) A. Magnetic susceptibility and neutron diffraction experiments suggest a spin-glass ground state for InVO3.

A phase diagram for CaCu x Mn 7 - x O 12 for x ⩽ 0.7 is presented. At room temperature CaCu x Mn 7 - x O 12 with x = 0.10 and 0.20 crystallizes in the trigonal space group R 3 ¯ and shows the same charge ordering of Mn 3 + and Mn 4 + ions as has been found for undoped CaMn 7 O 12 . The x = 0.10 and 0.20 compounds both show an apical-type Jahn–Teller distortion of the MnO6 octahedra around Mn 3 + ions. Both compounds undergo a structural phase transition to a high-temperature cubic structure (space group I m 3 ¯ ) with coexistence of both phases between 375 and 415 K for x = 0.10 and between 10 and 380 K for x = 0.20 . The domain sizes of the coexisting phases are at least 200 nm for both x = 0.10 and 0.20 compounds.

Here, we report a synthetic strategy to control the B-site ordering of the transition metal-doped perovskite-type oxides with the nominal formula of BaCa(0.335)M(0.165)Nb(0.5)O(3-δ) (M = Mn, Fe, Co). Variable temperature (in situ) and ex situ powder X-ray diffraction (PXRD), selected area electron diffraction (SAED), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), scanning/transmission electron microscopy (SEM/TEM), and thermogravimetic analysis (TGA) were used to understand the B-site ordering as a function of temperature. The present study shows that BaCa(0.335)M(0.165)Nb(0.5)O(3-δ) crystallizes in the B-site disordered primitive perovskite (space group s.g. Pm3̅m) at 900 °C in air, which can be converted into the B-site 1:2 ordered perovskite (s.g. P3̅m1) at 1200 °C and the B-site 1:1 ordered perovskite phase (s.g. Fm3̅m) at 1300 °C. However, the reverse reaction is not feasible when the temperature is reduced. FTIR revealed that no carbonate species were present in all three polymorphs. The chemical stability of the investigated perovskites in CO2 and H2 highly depends on the B-site cation ordering. For example, TGA confirmed that the B-site disordered primitive perovskite phase is more readily reduced in dry and wet 10% H2/90% N2 and is less stable in pure CO2 at elevated temperature, compared to the B-site 1:1 ordered perovskite-type phase of the same nominal composition.

The structure of Na 2 Ti 2 Sb 2 O has been investigated by temperature-dependent powder neutron diffraction. Na 2 Ti 2 Sb 2 O crystallizes in I 4/ mmm symmetry. The structure of this phase can be viewed as an anti-K 2 NiF 4 type where Ti 3+ ion is located between two oxygen atoms forming a square-planar lattice. Powder neutron diffraction studies of Na 2 Ti 2 Sb 2 O indicate that this compound has a structural distortion in the [Ti 2 Sb 2 O] 2− layer at T ≈120 K. This transition corresponds well to the previously reported anomalous transition temperature of the magnetic susceptibility and electronic resistivity. Several models to explain the data are presented and discussed.

The magnetic structure of ScMnO{sub 3} was investigated using polycrystalline samples. Bulk magnetic measurements were carried out revealing a Neel temperature of 130 K, followed by two maxima at 58 K and 40 K. The high-temperature data indicate strong antiferromagnetic coupling between Mn{sup 3+} ions in the form of a large, negative {theta} = {minus}943(7) K. Powder neutron diffraction as a function of temperature disclosed magnetic long-range ordering below 130 K, where the chemical and magnetic unit cell have the same volume. A 120{degree} magnetic structure was found consistent with the triangular Mn{sup 3+} sublattice and frustrated antiferromagnetic nearest neighbor coupling. The orientation of the magnetic spins is temperature dependent below 70 K.

The hydrothermal reaction of manganese or vanadium oxides in the presence of organic cations leads to the formation of new layered structures. When nickel salts are hydrothermally reacted with tetramethylammonium permanganate a new orthorhombic form of nickel manganese oxide, NiMnO 3 H x (where x≤1) is formed. It readily chemically intercalates lithium; it has space group Cmc2 1 , a=2.861(1) A, b=14.650(1) A, and c=5.270(1) A. The magnetic properties of this compound are quite different from the ilmenite NiMnO 3 phase, showing paramagnetism above 390 K and more complex behavior below that temperature. The hydrothermal reaction of vanadium pentoxide with methylamine leads to a series of new layered vanadium oxides, which differ in structure from the corresponding ones prepared in the presence of the tetramethylammonium ion because of the existence of hydrogen bonding. Methylamine is the first organic to form a double sheet vanadium oxide, (CH 3 NH 3 ) 0.75 V 4 O 10 ·0.67H 2 O, with the δ-Ag x V 2 O 5 structure. (CH 3 NH 3 ) 0.75 V 4 O 10 ·0.67H 2 O is monoclinic, space group C2/m with a=11.673(1) A, b=3.668(1) A, c=11.095(1) A and β=99.865(5)°. (CH 3 NH 3 )V 3 O 7 shows significant buckling of the layers compared with N(CH 3 ) 4 V 3 O 7 , and has a monoclinic unit cell, space group P2 1 /c with a=11.834(8) A, b=6.663(4) A, c=15.193(9) A and β=138.104(1)°.

The novel oxide defect fluorite phase ScTiO(3.5) is formed during the topotactic oxidation of ScTiO(3) bixbyite. We report the oxidation pathway of ScTiO(3) and structure evolution of ScTiO(3.5), Sc(4)Ti(3)O(12), and related scandium-deficient phases as well as high-temperature phase transitions between room temperature and 1300 °Cusing in-situ X-ray diffraction. We provide the first detailed powder neutron diffraction study for ScTiO(3). ScTiO(3) crystallizes in the cubic bixbyite structure in space group Ia3 (206) with a = 9.7099(4) A. The topotactic oxidation product ScTiO(3.5) crystallizes in an oxide defect fluorite structure in space group Fm3m (225) with a = 4.89199(5) A. Thermogravimetric and differential thermal analysis experiments combined with in-situ X-ray powder diffraction studies illustrate a complex sequence of a topotactic oxidation pathway, phase segregation, and ion ordering at high temperatures. The optimized bulk synthesis for phase pure ScTiO(3.5) is presented. In contrast to the vanadium-based defect fluorite phases AVO(3.5+x) (A = Sc, In) the novel titanium analogue ScTiO(3.5) is stable over a wide temperature range. Above 950 °C ScTiO(3.5) undergoes decomposition with the final products being Sc(4)Ti(3)O(12) and TiO(2). Simultaneous Rietveld refinements against powder X-ray and neutron diffraction data showed that Sc(4)Ti(3)O(12) also exists in the defect fluorite structure in space group Fm3m (225) with a = 4.90077(4) A. Sc(4)Ti(3)O(12) undergoes partial reduction in CO/Ar atmosphere to form Sc(4)Ti(3)O(11.69(2)).

The new pnictide oxide Sr2MnZn2As2O2 is reported. The crystal structure of this compound consists of a 1:1 intergrowth of square-planar MnO22- layers and ThCr2Si2-type Zn2As22- layers interspersed by Sr cations. This compound has been prepared by sintering the stoichiometric ratio of SrO, Mn, Zn, and As in a fused-silica ampule under 0.2 atm of Ar at 1000 °C for 1 week. The sample quality has been examined by Rietveld refinement of the powder X-ray diffraction data, and the transition metal site (2a and 4d) selectivity has been analyzed by Rietveld refinement of powder neutron diffraction data. Furthermore, effects of this structural order on the magnetic susceptibility and interaction between the magnetic layers have been analyzed by temperature-dependent magnetization measurements. The magnetic structures of both phases, A2MnZn2As2O2 (A = Sr, Ba), have been investigated by temperature-dependent powder neutron diffraction. The Ba analogue exhibits two-dimensional short-range order below about 40 K, where...

We report the formation pathway of ScVO(4) zircon from ScVO(3) bixbyite with emphasis on the synthesis and stability of the novel intermediate defect zircon phase ScVO(4-x) (0.0 < x

The rhombohedral CaMn7O12 manganite is an important material which shows magnetoelectrioc coupling with very high values of the electric polarization [1]. These outstanding properties motivated many experimental studies and also theoretical analysis. The mechanism which leads to these extraordinary properties has not been explained up to now. A fundamental information needed for such studies is the crystal structure and the magnetic ordering. CaMn7O12 has a complex structure with a magnetic moments modulation below TN=90K [1,2], a modulation of the atomic positions below TC=250K [2] and also orbital ordering. The magnetic modulation propagation vector qm is related with the atomic positions modulation vector qp by the relation qp=2qm [2]. This 2:1 relation is valid across a large range of temperatures and show the importance of spin-lattice coupling. The crystal and magnetic structure of CaMn7O12 was studied by neutron powder diffraction at the instrument DMC at SINQ [3]. The magnetic and atomic position modulations are described by using the superspace group formalism. This approach is especially important for description of both modulations with the same model [2]. The resulting magnetic ordering model obtained in [3] is more precise as compared with earlier works [1,2]. The present results [3] differ from those published by other authors [1]. The important difference is that in the present studies the angle, Phi, between Mn3+ and Mn4+ magnetic moments located in the same (001) planes (Phi = 0.99(2)Pi), i.e. the moments are antiparallel, whereas Johnson et al. [1] determined this angle as Phi=0.84(4) Pi. This angle is an important parameter of the model Hamiltonians describing the electronic and magnetic properties of CaMn7O12.