Phase relations in the dioxide-trioxide region of some 3d transition Metal-WO ternary systems

The phases occurring in the MnWO, FeWO, CoWO, and NiWO systems at 1373°K have been determined using X-ray diffraction and electron and optical microscopy. Experimentally most attention was given to the MnWO system, where it was found that Mn entered as the Mn²⁺ ion into the WO₃ host matrix and formed a perovskite-related bronze Mn_xWO₃. The highest observed x-value in the bronze is about 0.027. In addition a metastable θ_w(Mn) oxide with the Mo₅O₁₄ structure and a disordered oxide of overall composition approximately (Mn, W)O_2.82 were found. The FeWO system was similar to the MnWO system but significant differences occurred in the CoWO and NiWO systems where M_xWO₃ bronze phases were not observed to form at 1373°K. The stability of the M_xWO₃ and the θ_w(M) oxides formed are discussed in terms of the ionic size of the M ions involved. It is suggested that M_xWO₃ bronzes are metastable if these M ions are small.     

Crystallographic shear in the Nb2O5WO3 and Ta2O5WO3 systems

Crystallographic shear (CS) phases occurring in the Nb₂O₅WO₃ and Ta₂O₅WO₃ systems near to WO₃ were characterized by X-ray diffraction and high-resolution transmission electron microscopy. The Nb₂O₅WO₃ samples were heated at 1600K. They contained ordered {104} and {001} CS planes and wavy CS which were composed of intergrowths of {104} and {001} CS segments. The composition range over which the {104} CS series extended was from (Nb,W)O_2.954 i.e., (Nb,W)₆₅O₁₉₂, to (Nb,W)O_2.942, i.e., (Nb,W)₅₂O₁₅₃. The composition range over which the {001} CS series extended was from (Nb,W)O_2.9375, i.e., (Nb,W)₁₆O₄₇ to (Nb,W)O_2.875, i.e., (Nb,W)₈O₂₃. The Ta₂O₅WO₃ samples were prepared at 1593, 1623, and 1672K. At lower temperatures ordered {103} CS phases were found, with a composition range extending between (Ta,W)O_2.960, i.e., (Ta,W)₅₀O₁₄₈, to (Ta,W)O_2.944, i.e., (Ta,W)₃₆O₁₀₆. At 1673K ordered {103} CS phases occurred, as did wavy CS composed of intergrowths of {103} and {104} CS segments.     

The crystal structure of a complex cerium(III) molybdate; Ce6(MoO4)8(Mo2O7)

Ce₆Mo₁₀O₃₉ crystallizes in the triclinic system with unit-cell dimensions (from single-crystal data) a = 10.148(5), Å, b = 18.764(6), Å, c = 9.566(5), Å, α = 103.12(7)°, β = 78.07(7)°, γ = 107.69(7)°, and space group $\text{P}\text{1}\text{, z = 2}$. The structure was solved using direct methods with 3113 countermeasured reflections (MoKα radiation), and refined using Fourier and least-squares techniques to a conventional R of 0.039 (ωR = 0.047). Ce₆Mo₁₀O₃₉ has a structure that consists of isolated MoO₄ tetrahedra together with one corner-shared pair of tetrahedra, linked to irregular eight-coordinate Ce(III) polyhedra. The average MoO distance of 1.77 Å, and average CeO distance of 2.52 Å are in good agreement with previously reported values.     

Cryoscopic studies in molten salts. Dissociation state of some alkali isopolymolybdates and some related molybdenum(VI) compounds in molten K2Cr2O7and KNO3

The dissociation state of the solutes M₂MoO₄, M₂Mo₃O₁₀, M₂Mo₄O₁₃, M₂Mo₅O₁₆ (MRb or Cs), Na₂CrO₄·MoO₃, K₂CrO₄·2 MoO₃, Cr₂Mo₃O₁₂ and V₂MoO₈ was studied cryoscopically in molten K₂ Cr₂O₇ and KNO₃ solvents. The freezing point depression, ΔT, of the solvents was obtained by measuring the cooling curves of the binary salt mixtures over unlimited range of solute concentration. The number of foreign ions obtained ν, showed that the solutes were either simply dissociated in the melt into the probable stable species (MoO₄)^2?, (Mo₃O₁₀)^2?, (Mo₄O₁₃)^2? and (Mo₅O₁₆)^2? or, in some cases after reactions and rearrangements, into (CrMo₂O₁₀)^2? heteropolyions. The solute V₂MoO₈, on the other hand, was found to dissolve without any apparent dissociation. An agreement between the experimental and calculated values of activity, a, based on the Temkin and Random Mixing models and that of Van't Hoff's equation support the proposed simple dissocia- tion scheme for K₂Cr₂O₇Cs₂MoO₄ system.     

Survey of the phase formation in the Yb2O3Ga2O3MO and Yb2O3Cr2O3MO systems in air at high temperatures (M: Co,Ni, Cu,and Zn)

The phase relations in the Yb₂O₃Ga₂O₃CoO system at 1300 and 1200°C, the Yb₂O₃Ga₂O₃NiO system at 1300 and 1200°C, the Yb₂O₃Ga₂O₃CuO system at 1000°C and the Yb₂O₃Ga₂O₃ZnO system at 1350 and 1200°C, the Yb₂O₃Cr₂O₃CoO system at 1300 and 1200°C, the Yb₂O₃Cr₂O₃NiO system at 1300 and 1200°C, the Yb₂O₃Cr₂O₃CuO system at 1000°C, and the Yb₂O₃Cr₂O₃ZnO system at 1300 and 1200°C were determined in air by means of a classical quenching method. YbGaCoO₄ (a = 3.4165(1) and c = 25.081(2) Å), YbGaCuO₄ (a = 3.4601(4) and c = 24.172(6) Å), and YbGaZnO₄ (a = 3.4153(5) and c = 25.093(7) Å), which are isostructural with YbFe₂O₄ (space group: $\text{R}\text{3}\text{m, a = 3.455(1)}$ and c = 25.109(2) Å, were obtained as stable phases. In the Yb₂O₃Ga₂O₃NiO system and the Yb₂O₃Cr₂O₃MO system (M: Co, Ni, Cu, and Zn), no ternary stable phases existed.     

New pseudo-one-dimensional metals: M2Mo6Se6 (M = Na,In, K,TI), M2Mo6S6 (M = K,Rb, Cs), M2Mo6Te6 (M = In,TI)

We present a new series of ternary chalcogenides, derived from divalent molybdenum: M₂Mo₆X₆. These compounds crystallize in a hexagonal lattice with a ≈ 9 Å, c ≈ 4.5 Å, and space group $\text{P6}{}_3\text{m}$. The compounds are characterized by clusters (Mo₃)¹_∞ in the form of linear chains, resulting from a linear condensation of Mo₆ octahedral clusters. The (Mo₃)¹_∞ clusters are well separated from each other, with the shortest MoMo intercluster distance larger than 6 Å. The resulting pseudo-one-dimensional structures show remarkable anisotropy of physical properties.     

Some studies on the solid solutions in the systems Sr2Nb2O7Eu2Nb2O7 and Sr2Ta2O7Eu2Ta2O7

Preparation of new solid solutions containing divalent europium have been tried in the systems Eu₂Nb₂O₇Sr₂Nb₂O₇ and Eu₂Ta₂O₇Sr₂Ta₂O₇. These solid solutions described as Eu_2xSr_2(1?x)M₂O₇ (M = Nb and Ta) exist in a pure orthorhombic phase in a limited region of x from 0 to about 0.5. The compounds with compositions close to Eu₂M₂O₇ exist but techniques have not been found to prepare them in pure form.     

Une nouvelle famille structurale: Les titanoniobates et titanotantalates A2Nb6TiO18 et A2Ta6TiO18

New ternary oxides A₂M₆TiO₁₈ (A = Rb, Cs; M = Ta, Nb) have been synthesized by reaction between M₂O₅ and TiO₂ oxides and A₂CO₃ carbonates. They crystallize in the hexagonal system in a cell of dimensions a and c near 7.5 and 8.2 Å, respectively. There is one formula unit in the cell, in good agreement with the observed densities 4.38 and 4.78 for A₂Nb₆TiO₁₈, 6.62 and 6.93 for A₂Ta₆TiO₁₈. The structure has been determined from powder diffraction patterns, from the 64 first reflections (i.e., 190 hkl), and refined to R₁ values ranging from 0.06 and 0.08. It can be described from a basic unit of composition (M₆O₂₄) formed of 3 × 2 octahedra of oxygen atoms, sharing edges and corners, with MO distances ranging from 1.8 and 2.2 Å. Relations with the hexagonal tungsten bronze and pyrochlore-type structures are discussed.     

Synthesis,X-ray diffraction and vibrational study of silicates and germanates isostructural with kentrolite Pb2Mn2Si2O9

New germanates Pb₂M^III₂Ge₂O₉ (M^III = Fe, Mn, Sc, In) and silicates Pb₂M^IIM^IVSi₂O₉ (M^II = Mg, Ni, Co, Cu for M^IV = Sn; M^II = Co, Ni for M^IV = Ti) have been synthesized by solid state reaction. Their X-ray powder diagrams may be indexed in the orthorhombic system and show that these compounds are isostructural with kentrolite Pb₂Mn₂Si₂O₉. Doubts are expressed about the published structure of kentrolite and it is shown that some aspects of the structure should be re-examined.The I.R. and Raman spectra of these compounds are fairly complicated, and their discussion is restricted to the region of SiO or GeO stretching frequencies. These spectra show the existence of a pyro-silicate or -germanate group. The symmetric and antisymmetric frequencies of the SiOSi bridge have been identified with the help of ²⁸Si³⁰Si isotopic shifts. Their difference ν_as?ν_sym depends on the ionic radius of the cations, and points to a non-linear bridge of the pyrosilicate group.     

The phase relations in the In2O3A2O3BO systems at elevated temperatures [A: Fe or Ga, B: Cu or Co]

The phase relations in the In₂O₃Fe₂O₃CuO system at 1000°C, the In₂O₃Ga₂O₃CuO system at 1000°C, the In₂O₃Fe₂O₃CoO system at 1300°C, and the In₂O₃Ga₂O₃CoO system at 1300°C were determined by means of a classical quenching method. InFeCuO₄ (a = 3.3743(4) Å, c = 24.841(5) Å), InGaCuO₄ (a = 3.3497(2) Å, c = 24.822(3) Å), and InGaCoO₄ (a = 3.3091(2) Å, c = 25.859(4) Å) having the YbFe₂O₄ crystal structure, In₂Fe₂CuO₇ (a = 3.3515(2) Å, c = 28.871(3) Å), In₂Ga₂CuO₇ (a = 3.3319(1) Å, c = 28.697(2) Å), and In₂FeGaCuO₇ (a = 3.3421(2) Å, c = 28.817(3) Å) having the Yb₂Fe₃O₇ crystal structure, and In₃Fe₃CuO₁₀ (a = 3.3432(3) Å, c = 61.806(6) Å) having the Yb₃Fe₄O₁₀ crystal structure were found as the stable ternary phases. There is a continuous series of solid solutions between InFeCoO₄ and Fe₂CoO₄ which have the spinel structure at 1300°C. The crystal chemical roles of Fe³⁺ and Ga³⁺ in the present ternary systems were qualitatively compared.     

Subsolidus equilibria in the system BaO.TiO2.Al2O3

The subsolidus phase equilibrium relations in the system BaO.TiO₂.Al₂O₃ have been investigated using conventional solid state reaction techniques and X-ray powder diffraction. The existence of three known ternary compounds, BaTi₅Al₂O₁₄, BaTiAl₆O₁₂, and Ba₃TiAl₁₀O₂₀, was confirmed and their stability relations were studied. Various tie-lines existing between the ternary compounds and the binary titanates and aluminates of barium were established and a subsolidus phase diagram showing the phase assemblages compatible at 1200°C is presented.     

Relations structurales entre U3O8 et quelques fluorures mixtes de formules M2M′3F11, MM′2F7 et MM′3F10

U₃O₈ oxide, as well as M₂M′₃F₁₁, MM′₂F₇ and MM′₃F₁₀ fluorides, with M = Rb, Tl, Cs, NH₄ and M′ = In, Lu, Yb, Tm, is described as the regular repetition according to the … A-A-A … sequence of identical and parallel sheets of edge-and corner-sharing M′F₇ or UO₇ pentagonal bipyramids and M′F₆ octahedra. M′ and U atoms are systematically located at the lattice points of a pseudohexagonal network, but in the fluorides some of these lattice points are vacant, producing hexagonal tunnels in which M atoms are located. It is shown that in the two kinds of compounds the same linear chains and M′₃X₁₇ groups of pentagonal bipyramids are present, and that the transformation of the U₃O₈ structure into the fluorides can be achieved by an ordered substitution of some linear … UOUO … chains by … M-M-M … chains. All these structures can be described with the same structural model based on the chemical twinning principle.     

Structural studies in the Li2MoO4MoO3 system: Part 1 the low temperature form of lithium tetramolybdate,LLi2Mo4O13

LLi₂Mo₄o₁₃ crystallizes in the triclinic system with unit-cell dimensions a = 8.578 Å, b = 11.450 Å, c = 8.225 Å, α = 109.24°, β = 96.04°, γ = 95.95° and space group $\text{P}\text{1}\text{, Z = 3}$. The calculated and measured densities are 4.02 g/cm³ and 4.1 g/cm³ respectively. The structure was solved using three-dimensional Patterson and Fourier techniques. Of the 2468 unique reflections collected by counter methods, 1813 with I ? 3σ(I) were used in the least-squares refinement of the model to a conventional R of 0.031 (ωR = 0.038). LLi₂Mo₄O₁₃ is a derivative of the V₆O₁₃ structure with oxygen ions arranged in a face-centred cubic type array with octahedrally coordinated molybdenum and lithium ions ordered into layers.     

Synthesis and crystal chemistry of BaNd2Ti3O10, BaNd2Ti5O14, and Nd4Ti9O24

Two new ternary compounds BaNd₂Ti₃O₁₀ (1:1:3) and BaNd₂Ti₅O₁₄ (1:1:5) have been identified in the BaONd₂O₃TiO₂ system. Single crystals of the compounds were grown and unit cell dimensions and space group symmetry were determined. BaNd₂Ti₃O₁₀ is orthorhombic with a = 3.8655 ± 0.0003, b = 28.156 ± 0.003 and c = 7.6221 ± 0.0007 Å and possible space groups are Cmcm or Cmc2. The compound melts congruently at 1640 ± 20°C. BaNd₂Ti₅O₁₄ is also orthorhombic with a = 22.346 ± 0.002, b = 12.201 ± 0.001 and c = 3.8404 ± 0.0003 Å and possible space groups are Pbam and Pba2. This compound melts congruently at 1540 ± 20°C. Single crystals of the binary compound Nd₄Ti₉O₂₄ were also grown and found to be orthorhombic with a = 35.289 ± 0.003, b = 13.991 ± 0.001, c = 14.479 ± 0.001 Å, space group Fddd.     

First example of monodispersed (Mo3Se3)1∞ clusters

The close relationship of the structure of ternary molybdenum chalcogenides to molecular cluster compounds suggests that these chalcogenides might be synthesized from such clusters or be solubilized as clusters. However, in contrast to molybdenum halide clusters which can be obtained in solution from the solid phase, many attempts to solubilize these chalcogenide clusters were unsuccessful. This is the first report that some of the pseudo-one-dimensional compounds (M₂Mo₆X₆, X = Se, Te; M = Li, Na) can be dissolved when exposed to highly polar solvents such as dimethylsulfoxide or N-methylformamide. We show using optical microscopy, TEM, and light scattering that some of these solutions contain individual (Mo₃X₃)¹_∞ chains. This is also the first example of a purely inorganic transition-metal polymer solution. The behavior with respect to flocculation is consistent with the double layer theory. We show that the (Mo₃X₃)¹_∞ chains can be oriented in solution.     

Synthesis and structural study of the new rare earth magnesium borates LnMgB5O10 (Ln = La, …, Er)

To obtain rare earth luminescent materials with weak concentration quenching, the B₂O₃-rich portion of the ternary diagram Ln₂O₃MgOB₂O₃ (Ln = rare earth) has been investigated. A ternary phase of composition LnMgB₅O₁₀ has been found for Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Er. These compounds all crystallize in the monoclinic space group $\text{P2}{}_1\text{c}$. The structure has been determined on a LaMgB₅O₁₀ crystal. A full-matrix least-squares refinement leads to R = 0.039. The structure can be described as being made of (B₅O₁₀^5?)_n two-dimensional layers linked together by the lanthanum and magnesium ions. The rare earth atom coordination polyhedra form isolated chains. These borates are isostructural with some rare earth cobalt borates.     

Preparation, crystal structure, and magnetic studies of Na3Fe2Mo5O16, a new oxide containing Mo3O13 clusters

The complex oxide Na₃Fe₂Mo₅O₁₆ has been synthesized, and its crystal structure was determined by single-crystal X-ray diffraction (space group (SG) P-3m1; a=5.7366(6) Å, c=22.038(3) Å; Z=2). The compound can be considered as a new structure type containing Mo₃O₁₃ cluster units, which can be derived from the Na₂In₂Mo₅O₁₆ structure model by doubling of the cell along the c-axis. Na₃Fe₂Mo₅O₁₆ crystallizes in centrosymmetric SG (P-3m1) and the positions of the sodium atoms are fully occupied in contrast to the proposed Na₂In₂Mo₅O₁₆ model SG (P3m1). Magnetic properties of Na₃Fe₂Mo₅O₁₆ were studied by superconducting quantum interference device measurements, revealing antiferromagnetic ordering below Tχ_max=10(1) K. Thermal stability in air was investigated by in situ high-temperature X-ray powder diffraction. Structural relationships to Na₂In₂Mo₅O₁₆ and NaFe(MoO₄)₂ are discussed.     

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.     

Bi2n+4MonO6(n+1) with n=3, 4, 5, 6: A new series of low-temperature stable phases in the mBi2O3 - MoO3 system (1.0<m<1.7): Structural relationships and conductor properties

Four low-temperature phases with compositions Bi₁₀Mo₃O₂₄, Bi₆Mo₂O₁₅, Bi₁₄Mo₅O₃₆ and Bi₈Mo₃O₂₁ have been prepared by the n-butylamine wet synthesis method. They have been characterized by powder X-ray diffraction and transmission electron microscopy, mainly by selected area electron diffraction. The four phases present a close structural relationship and a common basic fluorite-type structure and are members of a homologous series of phases with general formula Bi_2n+4Mo_nO_6(n+1), being n=3, 4, 5 and 6, respectively. The matrices relating their superstructures and the basic fluorite type unit cell are given, as well as a general one for the whole series. The conductor behavior of these phases is characterized by impedance spectroscopy being all these materials very good ionic conductors.