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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.

The ambient pressure cation disordered InVO

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 the synthesis, structure, and redox behavior of the cation-ordered tetragonal Sc

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.

Over the past two decades, the magnetic ground states of all rare-earth titanate pyrochlores have been extensively studied, with the exception of ${\mathrm{Sm}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$. This is, in large part, due to the very high absorption cross section of naturally occurring samarium, which renders neutron scattering infeasible. To combat this, we have grown a large, isotopically enriched single crystal of ${\mathrm{Sm}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$. Using inelastic neutron scattering, we determine that the crystal field ground state for ${\mathrm{Sm}}^{3+}$ is a dipolar-octupolar doublet with Ising anisotropy. Neutron diffraction experiments reveal that ${\mathrm{Sm}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ orders into the all-in, all-out magnetic structure with an ordered moment of $0.44(7){\ensuremath{\mu}}_{B}$ below ${T}_{N}=0.35$ K, consistent with expectations for antiferromagnetically coupled Ising spins on the pyrochlore lattice. Zero-field muon spin relaxation measurements reveal an absence of spontaneous oscillations and persistent spin fluctuations down to 0.03 K. The combination of the dipolar-octupolar nature of the ${\mathrm{Sm}}^{3+}$ moment, the all-in, all-out ordered state, and the low-temperature persistent spin dynamics make this material an intriguing candidate for moment fragmentation physics.

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.

The crystal structure of α-Fe2O3and α-Cr2O3is usually described with the corundum-type trigonal crystal structure based on the space group R\bar 3c. There are, however, some observations of the magnetic ordering of both α-Fe2O3and α-Cr2O3that are incompatible with the trigonal symmetry. We show experimental evidence based on X-ray powder diffraction and supported by transmission electron microscopy that the symmetry of the crystal structure of both α-Fe2O3and α-Cr2O3is monoclinic and it is described with the space groupC2/c(derived from R\bar 3c by removing the threefold rotation axis). The magnetic orderings of α-Fe2O3and α-Cr2O3are compatible with the magnetic space groupsC2/candC2/c′, respectively. These findings are in agreement with the idea from Curie [(1894),J. Phys.3, 393–415] that the dissymmetry of the magnetic ordering should be associated with a dissymmetry of the crystal structure.

A few thallium based layered chalcogenides of α-NaFeO

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.

In(HfMg)0.5Mo3O12, which can be considered as a 1:1 mole ratio solid solution of the low-positive thermal expansion material HfMgMo3O12 and the low-negative thermal expansion (NTE) material In2Mo3O12 was prepared. From DSC and XRPD results, we show that In(HfMg)0.5Mo3O12 exists in a monoclinic (P21/a) structure at low temperature and undergoes a phase transition at ~425 K to an orthorhombic phase (Pnma), with an associated enthalpy change of 0.89 kJ mol−1. Thermal expansion is large and positive in the low-temperature monoclinic phase (average αl = 16 × 10−6 K−1 and 20 × 10−6 K−1, from dilatometry and XRPD, respectively). Remarkably, this material has a near-zero thermal expansion (ZTE) coefficient over the temperature range ~500 to ~900 K in the high-temperature orthorhombic phase, both intrinsically and for the bulk sample. The average linear intrinsic (XRPD) value is αl = −0.4 × 10−6 K−1, and the average bulk (dilatometric) value is αl = 0.4 × 10−6 K−1 with an uncertainty of ± 0.2 × 10−6 K−1. The slight difference between intrinsic and bulk thermal expansion is attributed to microstructural effects. XRPD results show that the thermal expansion is more isotropic than for the parent compounds HfMgMo3O12 and In2Mo3O12.

Polycrystalline Pb3TeCo3V2O14, a structural analogue of the multiferroic Ba3NbFe3Si2O14, was synthesized and characterized using X-ray diffraction, magnetic susceptibility, specific heat, dielectric constant, and neutron diffraction. Magnetic susceptibility, specific heat capacity measurements, and bond valence analysis confirmed that the V5+ ion is nonmagnetic, while Co2+ is in its high spin state (S = 3/2). Two magnetic transitions were seen at TN1 = 8.6 K and TN2 = 6.0 K where the spins first adopt a magnetic structure with propagation vector k = (0.752,0,1/2) and reorder into a commensurate structure with propagation vector k = (5/6,5/6,1/2). Changes in the dielectric constant at both magnetic phase transitions suggest that magnetoelectric coupling exists in Pb3TeCo3V2O14.

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 modulation of atomic positions in CaCu x Mn7−x O12 (x = 0 and 0.1) was studied using synchrotron radiation powder diffraction below 250 and 220 K, respectively. The copper-rich member CaCu x Mn7−x O12 (x = 0.23) does not show any modulation of the atomic positions at temperatures as low as 10 K. Using low-temperature neutron powder diffraction the modulation of the magnetic moments of Mn ions in CaCu x Mn7−x O12 (x = 0, 0.1 and 0.23) has been investigated. Long-range modulated magnetic ordering in CaCu x Mn7−x O12 (x = 0, 0.1 and 0.23) is observed below 90.4, 89.2 and 78.1 K. (0,0,q p) and (0,0,q m) are the propagation vectors describing the modulations of the atomic positions and the magnetic moments. For CaCu x Mn7−x O12 (x = 0 and 0.1) the magnetic modulation and atomic modulation lengths are related by a factor of 2 satisfying the relation (1 − q p) = 2(1 − q m).

We report the crystal structure evolution of CaCu0.2Mn6.8O12 as a function of temperature between 10 K and 290 K. The analysis of the diffraction data is carried out with the Rietveld method applied to the average trigonal structure of CaCu0.2Mn6.8O12. The x = 0.2 member shows similar low temperature extrema for the unit cell parameter evolution as the previously reported x = 0.1 and x = 0 members of the CaCuxMn7−xO12 system. All magnetic and crystallographic transition temperatures indicated by the unit cell parameter evolution obtained by powder X-ray diffraction methods systematically decrease with increasing Cu content, x.

The crystal structure of NdFeO3 has been studied by high resolution synchrotron powder X-ray diffraction in the range from 10 K to 750 K and laboratory X-ray powder diffraction in the range from 700 K to 1200 K. The refined a and c lattice parameters are monotonically increasing, whereas the b parameter goes through a maximum at around 40 K and a broad minimum at 160 K. No lattice parameter anomalies have been found around the Neel temperature TN = 687 K. The Nd3+ position is being reported for the temperature range from 10 K to 300 K.

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.

The perovskite Ba3ZnTa2O9 (BZT) is the parent of a family of high dielectric constant, low-loss oxides currently applied in mobile telecommunications base stations. The preparation of BZT microwave dielectric resonators with optimal dielectric properties requires careful attention to thermal treatment to control the formation of domains in which the Ta and Zn cations order on the octahedral sites of the perovskite structure. In this paper we use powder X-ray and neutron diffraction together with X-ray fluorescence and electron microscopy to demonstrate the strong correlation between the size of the cation-ordered domains, the extent of the ordering within them, and their composition, particularly the ZnO content. Phase separation into two trigonal BZT phases, which differ in the extent of cation order and the size of the ordered domains, is a common feature of all the synthetic procedures. A zinc-deficient impurity phase of nominal stoichiometry Ba8ZnTa6O24, involving face- as well as corner-sharing octah...

Polycrystalline samples of BaLaMnO4, oxygen deficient and oxygen excess BaLaMnO4 ± δ and the solid solution BaxSr1 − xLaMnO4 have been prepared and investigated. Magnetic susceptibility, powder X-ray diffraction and variable temperature powder neutron diffraction data are presented for these compounds. BaLaMnO4 and BaLaMnO3.89 crystallize in space group I4/mmm with unit cell constants a = 3.90252(6) A, c = 13.2660(3) A and a = 3.9089(1) A, c = 13.3243(5) A. The unit cell constants for the tetragonal BaLaMnO4.1 are a = 3.9314(2) A, c = 13.051(1) A. For the δ = 0.00 compound a small ferromagnetic response appears in the susceptibility below 300 K and the Curie–Weiss θ = +5 K but no evidence for long range magnetic order of any type is seen above 6 K in neutron diffraction data. The ferromagnetic response is supressed in the reduced form, BaLaMnO3.89, but is enhanced in the oxidized form, BaLaMnO4.1, with the ferromagnetic onset moving to 350 K. The solid solution BaxSr1 − xLaMnO4 (0.00 ≤ x ≤ 0.34) also crystallizes in space group I4/mmm. We find antiferromagnetic long range ordering for SrLaMnO4 (x = 0.0), ordering vector k = [1/2 1/2 0], with TN = 128 K and a Mn3+ moment of 3.3 μB, contrary to a previous report. The Neel temperatures and ordered moment magnitudes decrease as the Ba concentration is increased from x = 0.00 to x = 0.29. For x > 0.29 all signs of antiferromagnetic long range order vanish. An explanation for the destruction of three-dimensional (3D) magnetic long range ordering is proposed based on the distance dependence of the 2D in-plane correlation length, the interplanar exchange coupling and competing interactions.

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 compounds Na2Ti2Pn2O (Pn = As, Sb) crystallize in the anti-K2NiF4 structure type in the space group, I4/mmm, with Z = 2 and the lattice parameters a = 4.0810(9) A and c = 15.311(3) A for the As analogue at 310 K and a = 4.160(2) A and c = 16.558(7) A for the Sb analogue at 150 K. The structure consists of edge-shared [Ti4/2Pn2O4/4]2- layers separated by double layers of Na+. These compounds exhibit an anomalous transition in the temperature-dependent magnetic susceptibility at = 330 K for the As analogue and = 120 K for the Sb analogue. Temperature-dependent powder neutron diffraction has been performed to investigate the magnetic spin ordering and structure symmetry breakdown of the compounds; however, no scattering due to magnetic spin ordering or symmetry change has been detected. The temperature-dependent electrical resistivity of these compounds also exhibits an anomaly reminiscent of CDW (charge-density-wave)/SDW (spin-density-wave) materials. The As analogue shows an insulator-to-insulator tran...

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...

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)).

Copper–manganese oxides were analyzed by in situ high-temperature powder neutron and X-ray diffraction to investigate their crystal structure. Cu–Mn spinel was found to form a continuous solid solution with cubic symmetry between Mn3O4 and Cu2MnO4. A high-temperature phase with approximate composition Cu5Mn4O9 was shown to have hexagonal symmetry. The cation distribution and lattice parameters of Cu–Mn spinel were resolved through Rietveld refinement of in situ neutron diffraction data. The results demonstrated that the Cu ion has a lower octahedral site preference than manganese ions, and quenching is not a reliable method to determine the equilibrium structure in the system.

A new ScVO3 perovskite phase is synthesized from the cation-disordered bixbyite-type ScVO3 at 8 GPa and 1073 K.

Low temperature atomic position modulations and magnetic moment modulations are reported for CaCu(x)Mn(7 - x)O(12) (x = 0.0, 0.1 and 0.23) using neutron powder diffraction. Both modulations are described with propagation vectors (0, 0, q) parallel to the c-axis in the hexagonal setting. The present neutron diffraction studies confirm the quantitative model describing the atomic position modulations in CaCu(x)Mn(7 - x)O(12) (x = 0.0 and 0.1) as derived from synchrotron based powder x-ray diffraction studies (Sławiński et al 2009 Acta Crystallogr. B 65 535). Neutron diffraction studies confirm the relation between the atomic position modulation length L(p) and the magnetic modulation length L(m) = 2L(p) between 50 K and the Néel temperature T(N). CaCu(x)Mn(7 - x)O(12) (x = 0.1 and 0.23) shows a magnetic phase transition near 50 K associated with considerable changes of the magnetic modulation length and the magnetic coherence length, similar to that observed in the parent CaMn(7)O(12).

A novel ScVO 3 perovskite phase has been synthesized at 8 GPa and 1073 K from the cation-disordered bixbyite-type ScVO 3. The new perovskite has orthorhombic symmetry at room temperature, space group Pnma, and lattice parameters a = 5.4006(2) Å, b = 7.5011(2) Å, and c = 5.0706(1) Å with Sc 3+ and V 3+ ions fully ordered on the A and B sites of the perovskite cell. The vanadium oxygen octahedra [V-O 6] display cooperative Jahn-Teller (JT) type distortions, with predominance of the tetragonal Q 3 over the orthorhombic Q 2 JT modes. The orthorhombic perovskite shows Arrhenius-type electrical conductivity and undergoes a transition to triclinic symmetry space group P-1 close to 90 K. Below 60 K, the magnetic moments of the 4 nonequivalent vanadium ions undergo magnetic long-range ordering, resulting in a magnetic superstructure of the perovskite cell with propagation vector (0.5, 0, 0.5). The magnetic moments are confined to the xz plane and establish a close to zigzag antiferromagnetic mode. © 2011 American Chemical Society.

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...

The compounds Na2Ti2Pn2O (Pn = As, Sb) crystallize in the anti-K2NiF4 structure type in the space group, I4/mmm, with Z = 2 and the lattice parameters a = 4.0810(9) A and c = 15.311(3) A for the As analogue at 310 K and a = 4.160(2) A and c = 16.558(7) A for the Sb analogue at 150 K. The structure consists of edge-shared [Ti4/2Pn2O4/4]2- layers separated by double layers of Na+. These compounds exhibit an anomalous transition in the temperature-dependent magnetic susceptibility at = 330 K for the As analogue and = 120 K for the Sb analogue. Temperature-dependent powder neutron diffraction has been performed to investigate the magnetic spin ordering and structure symmetry breakdown of the compounds; however, no scattering due to magnetic spin ordering or symmetry change has been detected. The temperature-dependent electrical resistivity of these compounds also exhibits an anomaly reminiscent of CDW (charge-density-wave)/SDW (spin-density-wave) materials. The As analogue shows an insulator-to-insulator tran...

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

We report the preparation and stability of ScVO 3.5+ x and the novel phase InVO 3.5+ x . A VO 3.5+ x ( A =Sc, In) defect fluorite structures are formed as metastable intermediates during the topotactic oxidation of A VO 3 bixbyites. The oxidation pathway has been studied in detail by means of thermogravimetric/differential thermal analysis and in-situ powder X-ray diffraction. The oxidation of the bixbyite phase follows a topotactic pathway at temperatures between 300 and 400 °C in air/carbon dioxide. The range of accessible oxygen stoichiometries for the A VO 3.5+ x structures following this pathway are 0.00⩽ x ⩽0.22. Rietveld refinements against powder X-ray and neutron data revealed that InVO 3.54 and ScVO 3.70 crystallize in the defect fluorite structure in space group Fm -3 m (227) with a =4.9863(5) and 4.9697(3)A, respectively with A 3+ /V 4+ disorder on the (4 a ) cation site. Powder neutron diffraction experiments indicate clustering of oxide defects in all samples. Bulk magnetic measurements showed the presence of V 4+ and the absence of magnetic ordering at low temperatures. Powder neutron diffraction experiments confirmed the absence of a long range ordered magnetic ground state.

We report the synthesis and formation mechanism of Sc (i-x )Lu x VO 3 (0.0 ≤ x ≤ 1.0) using in situ powder X-ray diffraction and bulk solid-state preparation methods. The reduction of the solid solution Sc (i-x )Lu x VO 4 (0.0 ≤ x ≤ 1.0) results in orthorhombic perovskites (space group Pnma) Sc 1-x )Lu x VO 3 for x ≥≥≥≥ 0.58 and cubic bixbyites (space group: Ia3) Sc (1-x )Lu x VO 3 for Sc-rich samples with x < 0.1. During the high-temperature synthesis, Sc-rich bixbyite structures are initially formed and in a second step Lu-rich perovskites are formed. This two-step process is followed by Sc-Lu exchange between the two initial phases as shown by time-resolved powder X-ray diffraction. The in situ diffraction studies provide the basis for the preparation of metastable bixbyite as well as thermodynamically stable perovskite and bixbyite phases. For the perovskite phases, low-temperature powder neutron diffraction data and dc magnetic susceptibility data show that the Neel temperatures for the canted antiferromagnets range from 50 K for x = 0.58 to 100 K for x = 0.9. The Neel temperatures correlate with the V-O-V bond angles in the orthorhombic structures. The magnetic structure evolution has been followed as a function of temperature using powder neutron diffraction. In contrast, the cation-disordered bixbyite phases do not undergo magnetic long-range ordering, even at temperatures as low as 3 K.

The perovskites PbFeO2F and 0.5PbFeO2F-0.5PbTiO3 were synthesized at high temperatures (1000°C) and high pressures (4 – 6 GPa). The crystal and magnetic structures were determined using powder neutron diffraction. Quenched PbFeO2F has the cubic perovskite-type, Pm3m, structure in which the Pb ion shifts from ideal A-site along the directions, which is in good accordance with a previous report. The magnetic structure is antiferromagnetic G-type with propagation vector k = (1/2 1/2 1/2) and an Fe3+ ordered moment of 3.83 μB at 283K. The Néel temperature is 655(5) K. Annealed PbFeO2F has a tetragonal perovskite-type structure at room temperature and transforms reversibly from tetragonal to cubic at approximately 470 K. A superlattice with dimensions a × a × 5c is observed both in electron and x-ray diffraction. The solid solution 0.5PbFeO2F-0.5PbTiO3 belongs to the non-centrosymmetric space group P4mm. The magnetic structure is G-type antiferromagnetic and shows a weak ferromagnetic moment at 4 K. Consequently, 0.5PbFeO2F-0.5PbTiO3 is simultaneously ferroelectric and a weak ferromagnet at low temperature. The Néel temperature is 450 K but the temperature dependence of the ordered Fe moment is anomalous.

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.

The crystal structure of CaCu3Ti4O12 has been studied using high resolution synchrotron radiation based x-ray powder diffraction. The observed x-ray diffraction patterns show pronounced Bragg peak asymmetries which should not be present assuming the commonly accepted cubic crystal structure of CaCu3Ti4O12 described by the space group Im-3. Several structural models are discussed. The first model assumes a coexistence of two phases with the cubic symmetry (both space group Im-3) and different lattice constants. The next models are based on subgroups of the cubic space group Im-3. The best agreement with the experimental data is found for the two-phase cubic model.

Bulk physical properties of layered pnictide-oxides, Na2Ti2Pn2O (Pn = As, Sb) have been characterized. Both As and Sb compounds exhibit anomalous transitions in temperature dependent magnetic susceptibility and electrical resistivity. The powder neutron diffraction data show no superlattice reflections indicative of long-range order. The origin of the physical property anomalies and structure-property relationship between As and Sb compounds are described in terms of a charge-density-wave/spin-density-wave mechanism.

The crystal structure of CaMn7O12 and CaCu0.1Mn6.9O12 has been studied by synchrotron radiation (SR) based powder x-ray diffraction and neutron powder diffraction in the temperature range from 10 K up to 290 K. The lattice parameter a exhibits a minimum at 45 K in CaMn7O12. The c lattice parameter in CaMn7O12 and CaCu0.1Mn6.9O12 has a maximum at the same temperature. Additional Bragg peaks have been found in the SR diffraction patterns in CaMn7O12 and CaCu0.1Mn6.9O12 below 250 K and 220 K, respectively. All diffraction peaks have been indexed as (h,k,l ± κ), where κ was equal to 0.079(15) for CaMn7O12 and 0.093(15) for CaCu0.1Mn6.9O12. The incommensurate low-temperature diffraction peaks are not observed in neutron diffraction patterns. This leads to the conclusion that the phase transition to the incommensurate structure is due to charge ordering rather than atomic position modulation. The charge ordering temperature coincides with dielectric constant changes of four orders of magnitude for CaMn7O12.