Neutron powder profile studies of the gamma uranium trioxide phases

Neutron powder profile studies show the existence of three phases in gamma uranium trioxide between 373°K and 77°K. The three phases are closely related and the transitions smooth and displacive. At 373°K, γ-UO₃ is tetragonal, with a = 6.9013 (5) and c = 19.9754 (18) Å, and space group $\text{I4}{}_1\text{amd(}\text{D}{}^{19}{}_{\mathrm{4h}}\text{)}$. At 323°K, γ-UO₃ becomes orthorhombic, space group F_ddd(D²⁴_2h), with the cell dimensions (293°K) a = 9.787 (3), b = 19.932 (4) and c = 9.705 (3) Å. There is a further transition between 293°K and 77°K, and, at 77°K, the orthorhombic dimensions of the pseudocell are a = 9.8225 (7), b = 19.8487 (15), and c = 9.6318 (7) Å. The neutron diffraction studies show that, in all three phases, the coordination polyhedra of the two crystallographically distinct uranium atoms are octahedral and (dodecahedral-2) respectively. At 293°K, the shortest UO distance is 1.796 (6) Å, and thus there are no pure uranyl bonds, in agreement with the infrared spectrum. The UO distances are precise to about ± 0.006 Å, about ten times the precision of an earlier X-ray single-crystal study, in which the conclusions were in conflict with the infrared spectrum. The structure is made up of parallel chains of edge-fused U(2) octahedra, cross-linked by U(1) dodecahedra. The atomic shifts are not great in going from 373°K to 77°K; at 293°K the data will refine in the pseudotetragonal cell as well as the true orthorhombic cell, and the 77°K data will refine in the F_ddd cell.     

The Structure,Characterization, and Magnetic Properties of Ca4–xNixIrO6 (x = 0.25, 0.5)

Ca_4–xNi_xIrO₆ (x = 0.25, 0.5) crystallizes with trigonal (rhombohedral) symmetry in the space group R3¯c, Z = 6, for Ca_3.75Ni_0.25IrO₆ a = 9.3013(1) Å, c = 11.1554(1) Å; for Ca_3.5Ni_0.5IrO₆ a = 9.2723(1) Å, c = 11.0825(1) Å. Ca_3.75Ni_0.25IrO₆ and Ca_3.5Ni_0.5IrO₆ are isotypic to compounds of the Sr₄PtO₆ structure type. The structure of Ca_3.75Ni_0.25IrO₆ has been solved by means of single crystal X-ray diffraction data analysis with the reliability factors of R = 0.019 and R_w = 0.022. Also, both structures have been determined by Rietveld refinement of powder X-ray diffraction data. The structure consists of chains of alternating face-sharing IrO₆ octahedra and (Ca/Ni)O₆ trigonal prisms. The chains are separated by the calcium cations which are in a distorted square antiprismatic coordination. Magnetic measurements revealed that both Ca_3.75Ni_0.25IrO₆ and Ca_3.5Ni_0.5IrO₆ follow Curie-Weiss behavior at high temperatures. Ca_3.75Ni_0.25IrO₆ undergoes a single antiferromagnetic transition at T_N = 5 K whereas Ca_3.5Ni_0.5IrO₆ undergoes two antiferromagnetic transitions at T_N1 = 13 K and T_N2 = 4 K.     

Cs4[IrO4], ein neues Iridat mit planarem Anion [IrO4]4−

Cs₄[IrO₄], a New Iridate with Planar Anion [IrO₄]^4? For the first time we obtained black single crystals of Cs₄[IrO₄] by heating intimate mixtures of CsO_0.52 and IrO₂ (molar ratio Cs : Ir = 4.30 : 1.00; “Ag-bomb”, 740°C/86 d). Cs₄[IrO₄] crystallizes monocline, C 2/m, with a = 1031.66(8) pm, b = 671.61(4) pm, c = 660.44(6) pm, b? = 108.118(7)° and Z = 2 in the K₄[IrO₄]-type. The structure has been determined by four-circle-diffractometer data (PW 1100 from Phillips, Ag? Kα , graphite) with 841 I₀(hkl) with I ≥ 3s?(F) (from 947 I₀(hkl) out of 3529 measured reflexes). The Madelung Part of Lattice Energy, MAPLE, Effective Coordination Numbers, ECoN, these via Mean Fictive Ionic Radii, MEFIR, are calculated and discussed.     

Ein neuer Strukturtyp bei Oxoiridaten mit quadratisch-planaren [IrO4]4−-Gruppen: K2Na2[IrO4], ein Raumnetz [Na2IrO4] mit Kanälen. (Mit einer Anmerkung zu Rb2Na2[IrO4])

A New Type of Structure in Oxoiridates with Square-planar Groups [IrO₄]^4?: K₂Na₂[IrO₄], a Network [Na₂IrO₄] with Channels (With a Remark on Rb₂Na₂[IrO₄]) For the first time magnificent dark red cuboid single crystals of K₂Na₂[IrO₄] were prepared by annealing intimate mixtures of a) KO_0.51, Na₂O₂, IrO₂ and Ir-powder (molar proportions 3.02 : 1.40 : 1.00 : 1.00; Ag-bomb, 740°C, 54 d) and of b) KO_0.51, Na₂O and IrO₂ (molar proportions K : Na : Ir = 2.20 : 2.20 : 1.00; Ag-bomb, 760°C, 57 d) respectively. The oxide crystallizes mP36, space group P2₁/c with a = 600.35(6) pm, b = 1111.2(1) pm, c = 933.0(1) pm and β = 113.14(1)°. Structure determination via four-circle diffractometer data (Siemens AED 2, Mo-Kα-Radiation) for all 2347 unique reflexions (merged from 9397 I_o(hkl) gave R = 0.0357 and R_w = 0.0340. K₂Na₂[IrO₄] crystallizes in a new type of structure. The oxide is antiferromagnetic as magnetic measurements showed (T_N = 32 K, Θ = ?60.2 K (single crystals) and ?49.2 K (powder) respectively, μ = 3.06 μ_B (single crystals) and 2.93 μ_B (powder) respectively). Effective coordination numbers ECoN, mean fictive ionic radii MEFIR and the Madelung part lattice energy MAPLE as well as the charge distributions CHARDI and CHARDINO are calculated and discussed.     

High-pressure crystal growth and magnetic and electrical properties of the quasi-one dimensional osmium oxide Na2OsO4

Na₂OsO₄ crystals were grown by a NaCl flux method under high pressure. It crystallizes in the Ca₂IrO₄-type structure without having additional elements or metal vacancies, which are usually accommodated. It appears that Na₂OsO₄ is a metal-stoichiometric Ca₂IrO₄-type compound never been synthesized to date. Na₂OsO₄ has the octahedral environment of Os⁶⁺O₆ so that the electronic configuration is 5d², suggesting the magnetic S=1 ground state. However, magnetization, electrical resistivity, and specific heat measurements indicated that the non-magnetic S=0 state is much likely for Na₂OsO₄ than the S=1 state. Band structure calculations and the structure analysis found that the disagreement is probably due to the statically uniaxial compression of the OsO₆ octahedra, resulting in splitting of the t_2g band.     

Proton NMR studies of lanthanum nickel hydride: Structure and diffusion

The proton magnetic resonance spectrum of lanthanum nickel hydride LaNi_5.3H₆ was measured over the temperature range 118°K < T < 300°K. The second moment of the absorption at 118°K is M₂ = 13.4 ± 0.3 G². Several possible arrangements of the hydrogen atoms are discussed. Narrowing of the line above 140°K is analyzed in terms of proton diffusion and gives an activation enthalpy E = 21 ± 1 kJ mol^?1, NMR correlation time pre-exponential 0.2 ps < τ_c⁰ < 1.6 ps and a self diffusion coefficient at 300°K of 2 × 10^?12 m² s^?1 < D < 2 × 10^?11 m² s^?1.     

Crystal structure and magnetic properties of a one dimensional complex oxide ca3nimno6

The results of structural refinements and magnetic properties of one-dimensional oxide Ca₃NiMnO₆ are presented. The structure of Ca₃NiMnO₆ was solved by Rietveld analysis of powder neutron date in space group R-3c with a=9.1227(9) Å, c=10.5811(17) Å, z=6 (type of K₄CdCl₆). Infinite chains of MnO₆ octahedra and (Ni,Mn)O₆ trigonal prisms sharing faces run parallel to the c axis. The chains are separated by Ca²⁺ cations, which are located in a distorted square antiprismatic environment. Magnetic susceptibility obeys the Curie-Weiss law at 300–600 K with μ_eff value 5.00 μ_B consistent with the valence cationic combination Ni²⁺-Mn⁴⁺. Magnetic measurements display the antiferromagnetic ordering in Ca₃NiMnO₆ at 16 K.     

Halogénoacétates de cuivre(II): 2° Partie. Étude magnétique et spectroscopique

Electronic spectra of chloro- and bromoacetates of copper (II) (hydrated and as addition compounds with ethyl acetate) have been obtained in the solid state at 298 °K and 77 °K. The results are discussed and compared with magnetic susceptibility measurements. The band at about 27.5 kK. is present in the monomers and in the dimers and cannot be used to characterize the dimer species. It is assigned to the npπ → d_x²?y² symmetry forbidden transition.     

Mössbauer study of the thermal decomposition products of BaFeO4

A pure sample of a hexavalent iron compound, BaFeO₄, was decomposed at temperatures below 1200°C at oxygen pressures from 0.2 to 1500 atm. In addition to the already known BaFeO_x (2.5 ≦ x < 3.0) phases with hexagonal and triclinic symmetry, two new phases were obtained as decomposition products at low temperatures. One of the new phases, with composition BaFeO_{2.61 – 2.71}, has tetragonal symmetry; lattice constants are a₀ = 8.54 Å, c₀ = 7.29 Å. The phase is antiferromagnetic with Néel temperature estimated to be 225 ± 10 K. Two internal fields observed on its Mössbauer spectra correspond to Fe³⁺ and Fe⁴⁺. In the other new phase, with composition BaFeO_2.5, all Fe³⁺ ions had the same hyperfine field; it too is antiferromagnetic with a Néel temperature of 893 ± 10 K. Mössbauer data on the hexagonal phase coincided with earlier results of Gallagher, MacChesney, and Buchanan [J. Chem. Phys.43, 516 (1965)]. In the triclinic-I BaFeO_2.50 phase, internal magnetic fields were observed at room temperature, and it was supposed that there were four kinds of Fe³⁺ sites. The phase diagram of BaFeO_x system was determined as functions of temperature and oxygen pressure.     

Preparation and characterization of the Ti/IrO<Subscript>2</Subscript>/WO<Subscript>3</Subscript> as supercapacitor electrode materials

WO₃ films have been prepared onto IrO₂-coated Ti substrate by electro-deposition, and as-deposited and annealed films have been characterized by using Raman spectroscopy. It was found that the asdeposited film consists of orthorhombic WO₃ · H₂O phase, which transforms to amorphous WO₃ by annealing at 250°C and to monoclinic phase by annealing at and above 350°C. All electrochemical experiments were carried on Ti/IrO₂/WO₃ annealed at 450°C. The open-circuit potential could change significantly due to the hydration of the coating film. However this process is fairly slow. Reproducible voltammograms could be obtained quickly, further revealing high electrochemical stability of the Ti/IrO₂/WO₃ electrode. And the shapes of CV show the approximate rectangular mirror image, showing the typical characteristic of capacitive behavior. The specific capacitance obtained at a scan rate of 50 mV s⁻¹ is 46 F g⁻¹.     

Magnetic superexchange involving the oxygen-sulfur-oxygen pathway of the sulfate ion: A Mössbauer spectroscopy and magnetic susceptibility study of Fe(2,9-di-CH3-phenanthroline) SO4

Zero-field Mössbauer spectra of powder samples of Fe(2,9-di-CH₃-phenanthroline) SO₄ over the range 1.7 to 300°K show a large (～ 3.6 mm/sec) temperature-independent quadrupole splitting corresponding to an orbital singlet ground term. The chemical isomer shift, δ_FE=O, is 1.16 mm/sec (source and absorber at 4.2°K) corresponding to six coordinate high-spin iron (II). Below 4.2°K, the compound exhibits magnetic hyperfine splitting suggesting slow relaxation and the possibility of long-range three-dimensional magnetic ordering with a critical temperature T_c such that 3.5°K < T_c < 4.2°K and an internal hyperfine field H_n = 325 kG at 1.69°K. High-field Mössbauer spectra at 300°K indicate that the principal component of the electric field gradient tensor is positive and axial. Similar spectra at 4.2°K show an absence of nuclear Zeeman splitting for applied fields up to 60 kG, and indicate that at 4.2°K the material is rapidly relaxing but with substantial magnetic polarization and a negative internal hyperfine field. The temperature dependence of the magnetic susceptibility confirms antiferromagnetic interactions with a broad maximum χ′_M at ～ 11.8°K presumably due to low-dimensionality exchange interactions (possibly one) along MOSOM chains. Least-squares fits of χ′_M^?1 versus T for T50°K indicate (Curie-Weiss behavior with C = 3.26 emu/mole, θ = -21.95°K, and μ_eff = 5.11.     

Crystal field effects on the magnetic behavior of Yb2V2O7 and Tm2V2O7

The bulk magnetic behaviors of the pyrochlores Yb₂V₂O₇ and Tm₂V₂O₇ were investigated. Calculated susceptibilities were adjusted to obtain the best fit to experimental data. A cubic crystal field Hamiltonian was used with B°₄ = ?0.633 and B°₆ = 0.000705 K for Yb³⁺ and B°₄ = 0.0297 and B°₆ = 0.000339 K for Tm³⁺. The calculated susceptibility for Yb³⁺ was found to be insensitive to the addition of an axial B°₂ parameter to the cubic Hamiltonian.     

Phase relations in the pseudobinary system TiO2Ga2O3

Phase relations and microstructures in the TiO₂-rich part of the TiO₂Ga₂O₃ pseudobinary system have been determined at temperatures between 1373 and 1623°K using X-ray diffraction and electron and optical microscopy. The phases occurring in the system are TiO₂ (rutile), β-Ga₂O₃, a series of oxides Ga₄Ti_m?4O_2m?2 (m odd) which exist above 1463°K, and Ga₂TiO₅, which exists above 1598°K. The width of the phase region occupied by the Ga₄Ti_m?4O_2m?2 phases varies with temperature. At 1473°K it is narrow, and has limits of Ga₄Ti₂₅O₅₆ to Ga₄Ti₂₁O₄₈ while at higher temperatures it broadens to limits of from Ga₄Ti₂₇O₆₀ to Ga₄Ti₁₁O₂₈ at 1623°K. These phases are often disordered and crystals frequently contain partially ordered intergrowths of oxides with various values of m. On the TiO₂-rich side of the phase region there is a continuous change in texture from rutile to the end members of the Ga₄Ti_m?4O_2m?2 structures. The findings are summarized on a phase diagram.     

Synthesis of magnetoresistive glass ceramics based on (La,Sr)MnO3 in the La2O3-SrO-MnOx-SiO2-B2O3 system

Magnetic glass-ceramic composites containing micron-sized particles of lanthanum strontium manganite in the matrix of borate-silicate phases were prepared by thermal treatment of amorphous samples of nominal composition 28La₂O₃-22SrO-25MnO _x -17SiO₂-8B₂O₃at 800–1150°C. The samples obtained exhibit high magnetization up to 25 A m²/kg at a magnetic field strength of 720 kA/m. The relative magnetoresistance amounts to 17% at 77 K and a magnetic field strength of 160 kA/m.     

Studies of layered uranium(VI) compounds. III. Structural investigations of hydrogen uranyl phosphate and arsenate tetrahydrates below the respective transition temperatures of 274 and 301°K

The layered hydrates HUO₂PO₄·4H₂O (HUP), and HUO₂AsO₄·4H₂O (HUAs), which are protonconducting solid electrolytes above the conductivity transitions at 274 and 301°K, respectively, have been shown, using powder X-ray diffraction, to change from tetragonal to orthorhombic symmetry below these temperatures. For HUP the unit-cell dimensions were a = 6.985(5) and c = 17.45(1)Å at 290°K, and a = 6.966(5), b = 7.004(5), and c = 17.43(1)Å at 260°K. The values for HUAs were a = 7.150(2) and c = 17.608(5)Å, at 305°K, and a = 7.128(2), b = 7.168(2), and c = 17.613(5)Å at 293°K. The enthalpies of these displacive-type transitions were found from differential scanning calorimetry to be less than 0.5 kJ per mole of water for both compounds. Such a small value indicates that the rigid-like water lattices existing below the transitions do not become liquid-like above the transitions. The infrared spectra of HUP and HUAs both above the transitions, and down to 80°K, showed clear evidence of the presence of H₃O⁺ ions, showing that the conductivity transitions are not caused by a loss of carriers. Rather, the antiferroelectric ordering, known to exist for HUAs, would appear to cause the conductivity drop. Upon this indication of ordering within the water layers, two possible related H-bond ordered structures have been proposed which are consistent with the observed twinning behavior and cell symmetry. The same ordered structures are suggested for HUP from our observations of the twinning behavior.     

Two new organic–inorganic complexes associating the radical anion ABTS·– and the inorganic cation Ca2+: Ca0.55(ABTS)(H2O)x and Ca5(ABTS)6(H2O)29

The synthesis, crystal structure determination and physical properties of two new charge transfer salts containing the azinobisethylbenzothiazoline (ABTS) anion are described. Electrochemical oxidation in water of the diammonium salt of ABTS in presence of calcium chloride yields black single crystals of two new compounds with different morphologies. The needle-like crystals with Ca_0.55(ABTS)(H₂O)_x formula (x depending on the temperature) belong to the monoclinic symmetry, space group C2/c and cell parameters a=21.568(5), b=14.535(5), c=8.0278(17) Å, β=108.32(3)° at room temperature and a=22.180(4), b=14.288(3), c=8.0823(16) Å, β=108.13(3)°, with a lowering of the symmetry, space group Cc, at 200 K. The plate-shaped crystals formulated as Ca₅(ABTS)₆(H₂O)₂₉ belong also to the monoclinic symmetry with P2₁ space group and cell parameters a=11.222(2), b=37.991(8), c=19.327(4) Å, β=106.37(3)° at 200 K. The structure analysis of the first phase shows a one-dimensional character based on the stacking of organic molecules creating channels in which Ca²⁺ cations and water molecules are located. The second phase can be described as an alternation of organic and inorganic layers corresponding to a bidimensional hybrid network. The magnetic and electrical properties will be discussed.     

The preparation and characterization of CdVO3 prepared at ambient and high pressure

The solid state reaction of VO₂ and CdO yielded a phase of unknown structure, which transforms to CdVO₃(I) after treatment under 60–65 kbar pressure at 1200°C. The high-pressure product was characterized by crystallographic, electrical and magnetic properties. CdVO₃(I) is an orthorhombic perovskite-type compound and a metallic conductor, exhibiting Pauli paramagnetic behavior. In contrast, the ambient pressure phase displays Curie-Weiss magnetic behavior above 77°K.     

Subsolidus phase diagram of Cu2OCuOMoO3 system

Five chemical compounds, CuMoO₄, Cu₃Mo₂O₉, Cu₂Mo₃O₁₀, Cu₆Mo₄O₁₅, and Cu_4?x Mo₃O₁₂ (0.10 ? x ? 0.40), were identified in the system Cu₂OCuOMoO₃ and characterized by DTA, X-ray powder patterns, ir spectra, and magnetic properties. Cupric molybdates CuMoO₄ and Cu₃Mo₂O₉ are stable in air up to 820 and 855°C, respectively, melting at these temperatures with simultaneous decomposition (oxygen loss). Congruent mp of cuprous molybdates Cu₂Mo₃O₁₀ and Cu₆Mo₄O₁₅, in argon, are 532 and 466°C, respectively. Nonstoichiometric phase Cu_4?x Mo₃O₁₂ = Cu²⁺₃Cu⁰_1?xMo⁶⁺₃O₁₂, melts in argon between 630 and 650°C depending on the value of x and at 525–530°C undergoes polymorphic transformation. Areas of coexistence of the above-mentioned phases are determined. The μ_eff of Cu²⁺ ions and θ values are: 1.80 B.M. and 28°K for CuMoO₄, 1.71 B.M. and ? 12°K for Cu₃Mo₂O₉, and 1.74 B.M. and ? 93°K for Cu_4?xMo₃O₁₂. Below 200°K CuMoO₄ becomes antiferromagnetic. Cu₂Mo₃O₁₀ and Cu₆Mo₄O₁₅ show weak temperature-independent paramagnetism.     

Neutron and X-ray powder diffraction study of LixRuO2 and LixIrO2: The crystal structure of Li0.9RuO2

Compounds formed by the insertion of lithium into the rutile structure hosts RuO₂ and IrO₂ were studied by X-ray and neutron powder diffraction techniques. Compositions in the range Li_xMO₂, M = Ru or Ir, 0 < x < 1 are two-phase materials consisting of unreacted host, x = 0, and limiting compositions x = 0.9 in both cases. Preparation of compounds with x > 1 was unsuccessful. Li_0.9RuO₂ and Li_0.9IrO₂ have orthorhombic cells with a = 5.062(3), b = 4.967(4), c = 2.771(4) and a = 4.962(4), b = 4.758(4), c = 3.108(6), respectively. Compared to the host rutile (tetragonal) cells those of the insertion compounds are greatly expanded along [100] and [010], ～0.5 Å for both, and contracted along [001], by ～0.3 Å for Li_0.9RuO₂ and 0.05 Å for Li_0.9IrO₂. The space group for both insertion phases appears to be Pnnm, a subgroup of the rutile space group $\text{P4}{}_2\text{mnm}$. The structure of Li_0.9RuO₂ was solved from neutron diffraction data. Lithium exists as Li⁺ in octahedral sites. The LiO coordination is highly regular with two bonds at 2.05(1) Å and four at 2.08(2) Å. The overall structure is essentially an ordered NiAs-type very similar to but more regular than the previously reported LiMoO₂. Attempts to solve the structure of Li_0.9IrO₂ from both X-ray and neutron powder data were unsuccessful due, presumably, to severe preferred orientation.     

Solution precursor synthesis and magnetic properties of Eu1−xCaxTiO3

Europium titanate, EuTiO₃, is a paraelectric/antiferromagnetic cubic perovskite with T_N=5.5 K. It is predicted that compressive strain could induce simultaneous ferroelectricity and ferromagnetism in this material, leading to multiferroic behavior. As an alternative to epitaxial strain, we explored lattice contraction via chemical substitution of Eu²⁺ with the smaller Ca²⁺ cation as a mechanism to tune the magnetic properties of EuTiO₃. A modified sol-gel process was used to form homogeneously mixed precursors containing Eu³⁺, Ca²⁺, and Ti⁴⁺, and reductive annealing was used to transform these precursors into crystalline powders of Eu_1−xCa_xTiO₃ with x=0.00, 0.05, 0.10, 0.15, 0.25, 0.35, 0.50, 0.55, 0.60, 0.65, 0.80, and 1.00. Powder XRD data indicated that a continuous Eu_1−xCa_xTiO₃ solid solution was readily accessible, and the lattice constants agreed well with those predicted by Vegard's law. SEM imaging and EDS element mapping indicated a homogeneous distribution of Eu, Ca, and Ti throughout the polycrystalline sample, and the actual Eu:Ca ratio agreed well with the nominal stoichiometry. Measurements of magnetic susceptibility vs. temperature indicated antiferromagnetic ordering in samples with x≤0.60, with T_N decreasing from 5.4 K in EuTiO₃ to 2.6 K in Eu_0.40Ca_0.60TiO₃. No antiferromagnetic ordering above 1.8 K was detected in samples with x>0.60.