Phase formation in the Rb2MoO4-Er2(MoO4)3-Hf(MoO4)2 system and the crystal structure of new triple molybdate Rb5ErHf(MoO4)6

The subsolidus region of the Rb₂MoO₄-Er₂(MoO₄)₃-Hf(MoO₄)₂ ternary salt system is studied using X-ray powder diffraction. A novel 5: 1: 2 triple molybdate, Rb₅ErHf(MoO₄)₆, is found to form in the system. Crystals of Rb₅ErHf(MoO₄)₆ are flux-grown under spontaneous nucleation conditions. The composition and crystal structure of Rb₅ErHf(MoO₄)₆ are refined in a single-crystal X-ray diffraction experiment (X8 APEX diffractometer, MoK _α radiation, 1753 reflections, R = 0.0183). The crystals are trigonal; a = 10.7511(1) Å, c = 38.6543(7) Å, V = 3869.31(9) ų, d _calc = 4.462 g/cm³, Z = 6, space group $R\bar 3c$ . The mixed three-dimensional framework of the structure is formed of MoO₄ tetrahedra, each sharing corners with two ErO₆ and HfO₆ octahedra. Two types of Rb atoms occupy large cavities of the framework. The distribution of the Er³⁺ and Hf⁴⁺ cation over two positions is refined in the course of structure solution.     

Phase equilibria in the FeVO4-Fe2(MoO4)3 system

Phase équilibria have been investigated in the FeVO₄-Fe₂(MoO₄)₃ system for the whole concentration range of the components. In this system there is one compound which melts incongruently: Fe₄V₂Mo₃O₂₀. The results are presented in the form of a phase diagram.

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Zusammenfassung Phasengleichgewichte im System FeVO₄-Fe₂(MoO₄)₃ wurden über den ganzen Konzentrationsbereich der Komponenten hinweg untersucht. Eine Verbindung des Systems, Fe₄V₂Mo₃O₂₀, schmilzt inkongruent. Die Ergebnisse sind in Form eines Phasendiagramms angegeben.

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FeVO₄-Fe₂(MoO₄)₃ . Fe₄V₂Mo₃O₂₀, . .

     

Phase equilibria in the Tl2MoO4-Nd2(MoO4)3-Hf(MoO4)2 system and the crystal structure of double molybdate TlNd(MoO4)2

The Tl₂MoO₄-Nd₂(MoO₄)₃-Hf(MoO₄)₂ system was studied in the subsolidus region using X-ray powder diffraction. New triple molybdates were found to exist in this system: Tl₅NdHf(MoO₄)₆ (5: 1: 2), TlNdHf_0.5(MoO₄)₃ (1: 1: 1), and Tl₂NdHf₂(MoO₄)_6.5 (2: 1: 4). The first TlNd(MoO₄)₂ single crystals were grown from melt solutions with spontaneous nucleation. Their crystal structure was refined from X-ray diffraction data (Bruker X8 Apex automated diffractometer, MoK _α radiation, 386 F(hkl), R = 0.0136). The tetragonal unit cell parameters are as follows: a = 6.3000(2) Å, c = 9.5188(5) Å, V = 377.80(3) ų, Z = 2, ρ_calcd = 5.876 g/cm³, space group P4/nnc. The structure is a framework built of NdO₈ and TlO₈ tetragonal antiprisms linked via shared lateral edges and alternating in the checkerboard order. Layers share oxygen vertices with MoO₄ interlayer tetrahedra and are linked into the framework.     

Phase equilibria in the Tl2MoO4-Fe2(MoO4)3-Hf(MoO4)2 system and the crystal structure of ternary molybdate Tl(FeHf0.5)(MoO4)3

The subsolidus region of the ternary salt system Tl₂MoO₄-Fe₂(MoO₄)₃-Hf(MoO₄)₂ was studied by X-ray powder diffraction. New compounds Tl₅FeHf(MoO₄)₆ (5: 1: 2) and Tl(Fe,Hf_0.5)(MoO₄)₃ (1: 1: 1). were found to be formed in this system. Crystals of new ternary molybdate of the composition Tl(FeHf_0.5)(MoO₄)₃ were grown by spontaneous flux crystallization. Its composition and crystal structure were refined based on X-ray diffraction data. The mixed three-dimensional framework of the crystal structure is composed of Mo tetrahedra sharing O vertices with (Fe,Hf)O₆ octahedra. The thallium atoms occupy wide channels in the framework.     

Phase equilibrium in the Cs2MoO4-Bi2(MoO4)3-Zn(MoO4)2 system and the crystal structure of new triple molybdate Cs5BiZr(MoO4)6

The subsolidus region of the Cs₂MoO₄-Bi₂(MoO₄)₃-Zr(MoO₄) system was studied by X-ray powder diffraction. Quasi-binary sections were elucidated, and triangulation performed. Triple molybdates with the component ratios 5: 1: 2 (S ₁) and 2: 1: 4 (S ₂) were prepared for the first time. Crystals of cesium bismuth zirconium molybdate of the 5: 1: 2 stoichiometry (Cs₅BiZr(MoO₄)₆) were grown from fluxed melts with spontaneous nucleation. The composition and crystal structure of this triple molybdate were refined using X-ray diffraction data (collected on X8 APEX automated diffractometer, MoK _α radiation, 2348 F(hkl), R = 0.0226). The trigonal unit cell parameters were as follows: a = b = 10.9569(2), c = 39.804(4) Å, V = 4138.4(4) ų, Z = 6, space group R $ \bar 3 The subsolidus region of the Cs₂MoO₄-Bi₂(MoO₄)₃-Zr(MoO₄) system was studied by X-ray powder diffraction. Quasi-binary sections were elucidated, and triangulation performed. Triple molybdates with the component ratios 5: 1: 2 (S ₁) and 2: 1: 4 (S ₂) were prepared for the first time. Crystals of cesium bismuth zirconium molybdate of the 5: 1: 2 stoichiometry (Cs₅BiZr(MoO₄)₆) were grown from fluxed melts with spontaneous nucleation. The composition and crystal structure of this triple molybdate were refined using X-ray diffraction data (collected on X8 APEX automated diffractometer, MoK _α radiation, 2348 F(hkl), R = 0.0226). The trigonal unit cell parameters were as follows: a = b = 10.9569(2), c = 39.804(4) ?, V = 4138.4(4) ?³, Z = 6, space group R c. The mixed-metal three-dimensional framework in this structure is built of Mo tetrahedra and two sorts of (Bi,Zr)O₆ octahedra. Large interstices accommodate two sorts of cesium atoms. The Bi³⁺ and Zr⁴⁺ cation distributions over two positions were refined during structure solution. Original Russian Text ? B.G. Bazarov, T.V. Namsaraeva, R.F. Klevtsova, A.G. Anshits, T.A. Vereshchagina, R.V. Kurbatov, L.A. Glinskaya, K.N. Fedorov, Zh.G. Bazarova, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 9, pp. 1585–1589.     

Phase formation in the Ag3PO4-ScPO4 quasi-binary system

The phase formation in the subsolidus region of the Ag₃PO₄-ScPO₄ quasi-binary system was studied by X-ray powder diffraction and differential thermal analyses throughout the range of concentration ratios of the initial components at an interval of 10 mol % within the temperature range 20–1000°C in air at atmospheric pressure. A T-x section was constructed. The formation of the binary phosphate Ag₃Sc₂(PO₄)₃ melting incongruently at 1300 ± 5°C was detected. The composition of an eutectic (with the melting point 900 ± 5°C) is between those of the compounds Ag₃PO₄ and Ag₃Sc₂(PO₄)₃.     

Phase formation in the Ag3VO4-ScVO4 quasi-binary system

Subsolidus phase formation in the Ag₃VO₄-ScVO₄ quasi-binary system was studied using X-ray powder diffraction and DTA in air under atmospheric pressure over the entire range of component concentrations in 5 mol % steps between 20 and 800°C. Two compounds were found to form: Ag₃Sc(VO₄)₂ and Ag₃Sc₂(VO₄)₃, both melting incongruently at 750 ± 5 and 960 ± 5°C, respectively. A T-x diagram of the Ag₃VO₄-ScVO₄ quasi-binary system was constructed. A eutectic (T _m = 450 ± 5°C) is between the compounds Ag₃VO₄ and Ag₃Sc(VO₄)₂; Ag₃VO₄ concentration is ～5 mol %.     

Glass formation in the Al(IO3)3-Al2(SO4)3-H2O system

Glass-formation boundaries in the Al(IO₃)₃-Al₂(SO₄)₃-H₂O system are determined. The IR spectra of glassy and crystalline Al(IO₃)₃ · 8H₂O samples are measured. The structure and properties of glassy Al(IO₃)₃ · 10H₂O are compared to those of glassy Al₂(SO₄)₃ · 10H₂O.     

Phase relations in the systems M2MoO4-Cr2(MoO4)3-Zr(MoO4)2 (M = Li, Na, or Rb)

Phase equilibria in the systems M₂MoO₄-Cr₂(MoO₄)₃-Zr(MoO₄)₂ (M = Li, Na, or Rb) were investigated by X-ray powder diffraction analysis, DTA, and IR spectroscopy. The subsolidus structure of the phase diagrams of the systems under study was established. Two phases are formed in the Rb₂MoO₄-Cr₂(MoO₄)₃-Zr(MoO₄)₂ system with the molar ratios of the starting components equal to 5: 1: 1 (S ₂) and 1: 1: 1 (S ₁). Proceeding from that the isostructurality of Rb₅FeHf(MoO₄)₆ and S ₂ the unit cell, parameters are determined for S ₂.     

LiFe(MoO4)2, LiGa(MoO4)2 and Li3Ga(MoO4)3

The structures of lithium iron dimolybdate, LiFe(MoO₄)₂, and lithium gallium dimolybdate, LiGa(MoO₄)₂, are shown to be isomorphous with each other. Their structures consist of segregated layers of LiO₆ bicapped trigonal bipyramids and Fe(Ga)O₆ octahedra separated and linked by layers of isolated MoO₄ tetrahedra. The redetermined structure of trilithium gallium trimolybdate, Li₃Ga(MoO₄)₃, shows substitional disorder on the Li/Ga site and consists of perpendicular chains of LiO₆ trigonal prisms and two types of differently linked Li/GaO₆ octahedra.     

Phase formation in the systems Rb2MoO4-BaMoO4-R2(MoO4)3, R = Nd,Sm, Eu,Gd

Phase formation in the subsolidus area of the systems Rb₂MoO₄-BaMoO₄-R₂(MoO₄)₃ was studied by the methods of X-ray and differential-thermal analysis. In these systems ternary molybdates RbBaR(MoO₄)₃ crystallizing in the monoclinic crystal system (space group P2_1/n ) are formed. Their crystallographic parameters were calculated, and temperature dependences of the electrical conduction, dielectric permeability, and dielectric loss tangent were studied.     

Studies on the system CrVO4-Fe2(MoO4)3

X-RPD and DTA revealed that CrVO₄ reacts with Fe₂(MoO₄)₃ in the solid state to form Fe₂Cr₂V₂Mo₃O₂₀. The thermal and X-ray characteristics of this phase have been established.

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Zusammenfassung Mittels DTA und Debye-Scherrer-Untersuchungen wurde festgestellt, daß CrVO₄ und Fe₂(MoO₄)₃ im festen Zustand miteinander reagieren und Fe₂Cr₂V₂Mo₃O₂₀ bilden. Thermische und röntgenographische Eigenschaften dieser Phase wurden ermittelt.

     

Phase equilibria in the systems Rb2MoO4-R2(MoO4)3-Hf(MoO4)2 (R = Al, In, Sc, Fe(III)) and the crystal structure of double molybdate RbFe(MoO4)2

The systems Rb₂MoO₄-R₂(MoO₄)₃-Hf(MoO₄)₂ have been investigated in the subsolidus region by X-ray powder diffraction, DTA, and IR spectroscopy. Triple molybdates of the composition 5: 1: 2 are formed in the systems with R = Al, In, Sc, and Fe. Molybdates of composition 5: 1: 3 and 1: 1: 1 are found in the iron(III)-containing system in addition to the 5: 1: 2 molybdate. Single crystals of the double molybdate RbFe(MoO₄)₂, which is formed in the Rb₂MoO₄-Fe₂(MoO₄)₃ system, have been grown. The structure of this double molybdate has been refined using X-ray diffraction data (X8 APEX automated diffractometer, MoK _α radiation, 373 F(hkl), R = 0.0287). The trigonal unit cell parameters are the following: a = b = 5.6655(2) Å, c = 7.5061(4) Å, V = 208.65(1) ų, Z = 1, ρ_calc = 3.670 g/cm³, space group R3m1. The structure is formed by layers of FeO₆ octahedra sharing corners with MoO₄ tetrahedra and RbO₁₂ icosahedra.     

Phase equilibria in the KCl-KBO2-K2CO3-K2MoO4 quaternary system

The phase diagram of the quaternary system KCl-KBO₂-K₂CO₃-K₂MoO₄ was studied by a calculation-experimental method and differential thermal analysis. Analytical models of phase equilibrium states were obtained, and the coordinates of a quaternary eutectic were determined: 550°C, 50% KCl, 8% KBO₂, 23% K₂CO₃, and 19% K₂MoO₄.     

New MoO3 Phase:Synthesis and Structure of (NH4)0.66MoO3

Gentle reduction of solid MoO₃ leads to four distinct phase of H_xMoO₃. These compounds have a wide range of colors and crystal classes:phase Ⅰ (0.25< x< 0.40), blue, orthorhombic; phase Ⅱ (0.85< x< 1.04), blue, monoclinic; phase Ⅲ (1.55< x< 1.72), red, monoclinic; and phase Ⅳ (x=2.0), green, monoclinic^[1-3]. We have now obtained a new MoO₃ phase (NH₄)MoO₃ with network structure from an aqueous solution of Na₂MoO₄ reduced by NH₂NH₂·2HC1 at 170℃.     

The standard molar enthalpy of formation of Ce2(MoO4)3(s) and Sm2(MoO4)3(s) using solution calorimetry

The enthalpies of formations of Ce₂(MoO₄)₃(s) and Sm₂(MoO₄)₃(s) have been measured at 298.15 K using semi adiabatic solution calorimetry. The precipitation reaction between RE(NO₃)₃·6H₂O(s) (R= Ce, Sm) and ammonical solution of Na₂MoO₄(s) was studied. From the enthalpy of precipitation and other required auxiliary data, $ \Updelta_{\text{f}} H_{\text{m}}^{ \circ } \left( { 2 9 8. 1 5 {\text{ K}}} \right) $ Δ f H m ° ( 2 9 8.1 5 K ) of Ce₂(MoO₄)₃(s) and Sm₂(MoO₄)₃(s) have been calculated for the first time as ?4388.7 ± 3.6 and ?4363.4 ± 4.1 kJ mol^?1, respectively. The enthalpy of hydration of anhydrous Ce(NO₃)₃(s) to Ce(NO₃)₃·6H₂O(s) has been calculated. $ \Updelta_{\text{f}} H_{\text{m}}^{ \circ } \left( {{\text{MoO4}}^{ 2- } ,\,{\text{aq}},\, 2 9 8. 1 5 \,{\text{K}}} \right) $ Δ f H m ° ( MoO4 2 ? , aq , 2 9 8.1 5 K ) has also been measured and calculated as ?995.1 kJ mol^?1 from required literature data.     

Phase formation in the HfO(NO3)2-H3PO4-CsF(HF)-H2O system

The phase formation in the system HfO(NO₃)₂-H₃PO₄-CsF(HF)-H₂O was studied along the sections at the molar ratios PO ₄ ^3? /Hf = 0.5, 1.5, and 2.0 and RbF:Hf = 1?C5, and also in the presence of HF at CsF: Hf = 1. The initial solutions contained 2?C24 wt % HfO₂. The synthesis was performed at room temperature. The following substances were isolated: crystalline cesium fluorophosphate hafnates CsHf₂F₆PO₄ · 4H₂O, CsHfF₂PO₄ · 0.5H₂O, and CsH₂Hf₂F₂(PO₄)₃ · 2H₂O; X-ray amorphous cesium fluorophosphate hafnate of the average composition Cs₂Hf₃O_1.5F₅(PO₄)₂ · 5H₂O; and X-ray amorphous cesium fluorophosphate nitrate hafnate Cs₅H₄Hf₃F₇(PO₄)_3.66(NO₃)₃ · 5H₂O. The compositions of the amorphous phases should be refined. Cesium fluorophosphate hafnates were obtained for the first time. The compounds were studied by crystal-optical, elemental, X-ray diffraction, IR spectroscopic, and electron microscopic analyses.     

Phase formation in the ZrO(NO3)2-H3PO4-CsF(HF)-H2O system

The phase formation in the system ZrO(NO₃)₂-H₃PO₄-CsF(HF)-H₂O was studied at the molar ratio CsF/Zr = 1 along the sections PO ₄ ^3? /Zr = 0.5 and 1.5 at a ZrO₂ concentration in the initial solution of 2?C14 wt %. The following compounds were isolated: Cs₅Zr₄F₂₁ · 3H₂O, CsZr₂(PO₄)₃ · 2HF · 2H₂O, CsZrF₂PO₄ · H₂O, CsZr₂F₆PO₄ · 4H₂O (for the first time), CsHZrF₃PO₄ (for the first time), Cs_0.70ZrF(PO₄)_1.23 · nH₂O, and CsHZr₂F₂(P_O4)_2.66 · nH₂O. The compositions of CsZrF₂PO₄ · H₂O, Cs_0.70ZrF(PO₄)_1.23 · nH₂O, and CsHZr₂F₂(PO₄)_2.66 · nH₂O are conditional. All the compounds were characterized by crystal-optical, X-ray powder diffraction, thermal analyses, and IR spectroscopy. The formula CsHZrF₃PO₄ was established by energy-dispersive analysis with a LEO-1450 scanning electron microscope and an MS-46 CAMECA X-ray microanalyzer.     

Phase equilibria up to the solidus line in the V2O5−Cr2(MoO4)3 system

Phase equilibria being established in the subsolidus area of the V₂O₅?Cr₂(MoO₄)₃ system at the whole component concentration range have been studied basing on DTA and X-ray phase powder diffraction. It has been established that the system is not a real two-component system in the subsolidus area. The fact has been proved by the presence of fields in that area, where three solid phases remain in mutual equilibrium.     

Subsolidus area of the AlVO4−Al2(MoO4)3 system

The behaviour of Al₂(MoO₄)₃ towards AIVO₄ in the subsolidus area, over the whole component concentration range, has been studied using the DTA and XRD methods. The experimental results have been presented in the form of a phase diagram. It has been found that components of the system of interest do not remain in equilibrium, and AlVO₄?Al₂(MoO₄)₃ system is not a real two-component system, even in the subsolidus area.