Zur kenntnis von PbAl2Se4 und PbGa2Se4

The crystal structures of the already known compounds PbAl₂Se₄ and PbGa₂Se₄ have been solved. PbAl₂Se₄ crystallizes in the CaAl₂Se₄-structure (space group: Cccm, a = 636 ± 1 pm, b = 1063 ± 1 pm, c = 1078 ± 1 pm, N = 4). PbGa₂Se₄ crystallizes in the SrIn₂Se₄-structure (space group: Fddd, a = 2137 ± 2 pm, b = 2147 ± 2 pm, c = 1273 ± 1 pm, N = 32). Both structures are variants of the TlSe-type.     

Phase equilibrium diagram for the system Gd2O3-MoO3

Phase equilibria have been established in the binary system Gd₂O₃MoO₃ including Gd₂(MoO₄)₃ with ferroelectricity and ferroelasticity below 159°C, by means of differential thermal analysis and X-ray powder diffraction techniques. It is shown that Gd₂(MoO₄)₃ has no solubility of other compounds in this system and melts congruently on its stoichiometric composition. Three distinct intermediate compounds were found. Gd₂O₃.6MoO₃ and Gd₂O₃.4MoO₃ are formed by a peritectic reaction at 730°C and 825°C, respectively. The remaining compound Gd₂O₃.MoO₃ with the structure closely related to Eu₂O₃.MoO₃ does not decompose below 1400°C.     

Phase equilibrium and ionic conductivity in the PbF2YF3 system

The phase diagram of the PbF₂-YF₃ system has been studied by D.T.A. and X-ray diffraction techniques. A large domain of a fluorite-type solid solution Pb_1?xY_xF_2+x (0?x?0.39 at 885°C) called F has been isolated. A very small domain of a tysonite-type solid solution H only stable in a very narrow temperature range is also observed. Two ordered phases R and T, whose structures derive from the fluorite-type are identified. The transport properties of F, R and T are analyzed and compared to those of analogous phases belonging to other Pb_1?xM_xF_2+x systems (M = In, Sb, Bi). The influence of the polarizability of the substituent trivalent ion on the electrical properties is particularly discussed.     

Phase equilibrium of the Ag2O- TeO2- V2O5 system in the Ag2O rich region

Using DTA and X-ray phase analysis the phase equilibrium in the Ag₂O-TeO₂-V₂O₅ system has been studied in the region rich in Ag₂O. The section Ag₂O · V₂O₅ · 2TeO₂-Ag₂O · V₂O₅ was of simple quasibinary type with a eutectic point at about 60mol % Ag₂O·V₂O₅. The remaining sections showed a complex polythermal course. On the basis of the experiments carried out, the fields of initial crystallization of 12 crystal phases were outlined.     

Phase transition in V3O5

A phase transition at 420°K previously unreported, has been discovered in V₃O₅. The transition is characterized by an endothermic DTA peak on heating and an abrupt change in the electrical resistivity at the same temperature. Results from X-ray analysis of the V₃O₅ samples exhibiting the transition agree very well with the values reported by Andersson (1). Powder diffraction analysis of the high temperature phase indicates that there is a small change in the cell volume but the crystal apparently conserves its symmetry through the transition.     

Magnetic properties of quaternary compounds on the Cu2GeSe3-Cr2Se3 join of the Cu2Se-GeSe2-Cr2Se3 system

We have synthesized two quaternary compounds, Cu₂GeCr₄Se₉ and Cu₂GeCr₆Se₁₂, with compositions on the Cu₂GeSe₃-Cr₂Se₃ join of the Cu₂Se-GeSe₂-Cr₂Se₃ system. Their composition stability limits and the lattice parameters of Cu₂GeCr₄Se₉ have been determined, and their magnetic properties (magnetic moments, temperatures and types of magnetic transitions) have been investigated. Ferromagnetic samples with Curie temperatures from 95 to 135 K have been identified in the homogeneity ranges of the two compounds. Original Russian Text ? T.G. Aminov, G.G. Shabunina, E.V. Busheva, 2009, published in Neorganicheskie Materialy, 2009, Vol. 45, No. 3, pp. 283–287.     

V3.2W1.8O13 and studies of the V2O5WO3VO2 ternary system

The tungsten/vanadium ratios for the known ternary compounds in the V₂O₅WO₃VO₂ chemical system are characterized. The compounds V_2.5W_.5O₇ and V₂WO_7.5 are the n = m = 3 and n = m = 4 members of a sreies of M-niobia like crystallographic shear structures. We have found the n = m = 5 member of the series at the composition V_3.2W_1.8O₁₃, and report its crystallographic unit cell, powder x-ray diffraction pattern and range of temperature stability.     

Phase equilibrium and growth of homogeneous crystals in the γLa2S3  γNd2S3 system

T-x diagram of the γLa₂S₃  γNd₂S₃ system was plotted for the temperature interval 1400–2100°C. γLa₂S₃ and γNd₂S₃ form unlimited solid solutions of the substitution type. Basing on this phase diagram the theoretical distribution curves of Nd₂S₃ along the ingot of length were calculated. The experimental distribution curves were determined by chemical and electron microprobe measurements of La and Nd content in γ(La,Nd)₂S₃ ingots directionally solidified from the melt of different composition. Character of the component distribution in the ingots shows that diffusion of neodymium and lanthanum is exeptionally fast at 1700–2000°C. This phenomenon is explained by vacancy diffusion mechanism in γLa₂S₃  γNd₂S₃ solid solutions. Crystal structure of these solid solutions belongs to Th₃P₄ type with high concentration of randomly distributed cation vacancies.     

Synthesis and selected properties of CrSbVO6 and phase relations in the V2O5–Cr2O3–α-Sb2O4 system in the solid state

Phase relations in the ternary oxide system V₂O₅–Cr₂O₃–α-Sb₂O₄ in the solid state in the atmosphere of air have been investigated by using the XRD, DTA/TG and IRS methods. Obtained results have shown that in the system the compound CrSbVO₆ is formed. This compound has been obtained both from oxides and from a mixture comprising CrSbO₄, CrVO₄ and SbVO₅ as well as from mixtures: CrSbO₄/V₂O₅, CrVO₄/α-Sb₂O₄ and SbVO₅/Cr₂O₃. A Solid product of incongruent melting of CrSbVO₆ at ∼1300°C is Cr₂O₃. CrSbVO₆ crystallizes in the tetragonal system and its calculated unit cell parameters amount to: a = b = 0.45719(12) nm, c = 0.30282(8) nm, Z = 2. The obtained results have allowed us also to divide the investigated system V₂O₅–Cr₂O₃–α-Sb₂O₄ into seven subsidiary subsystems and to determine temperatures and components concentration range in which CrSbVO₆ remains at equilibrium in the solid state with other phases formed in corresponding binary systems.     

Système ternaire La2Se3-Ga2Se3-GeSe2 diagramme de phase — Etude des verres

Existence of a solid solution, hexagonal $\text{Ce}{}_6\text{Al}{}_{\mathrm{<mtext>10</mtext><mtext>3</mtext>}}\text{S}{}_{14}$-type, between $\text{La}{}_6\text{Ga}{}_{\mathrm{<mtext>10</mtext><mtext>3</mtext>}}\text{Se}{}_{14}$ and La₆Ge_2.5Se₁₄ compounds. Location of the eutectic valleys and ternary eutectic (650°C, for La₂Se₃, 3 Ga₂Se₃, 14 GeSe₂). Level curves of the liquidus.Obtention of glasses in a large domain of composition, along the eutectic valley. Measurements of Tg and crystallisation temperature.     

Studies on the system V3O5 /1b Ti3O5

The system (V_1?xTi_x)₃O₅ has been studied by means of X-ray powder photography, DTA and magnetic susceptibility measurements. A continuous series of solid solutions has been found for samples prepared at 1175 K, while samples prepared at 1275 K showed the solid solubility in the V₃O₅ end phase to be limited by $\text{x}\text{< 0.7}$ DTA studies have shown that the peak associated with the V₃O₅(low) /1b V₃O₅(high) transition disappears at $\text{x}\text{= 0.024}$. The DTA studies have also confirmed the existence of a phase transition in γ-Ti₃O₅ ($\text{x}\text{= 1}$) at 227 K.     

Thermodynamic properties of V3Te4

The heat capacity of V₃Te₄ has been measured as a function of temperature using an adiabatic calorimeter, and its thermodynamic properties were evaluated. We have determined the Debye characteristic temperature and fracton dimension of crystalline V₃Te₄.     

Phase diagram and thermodynamic properties in the VWO system at high temperatures I. In a region WWO2VO2V2O3

The phase relation within a region, WWO₂VO₂V₂O₃ in the VWO system, was examined at 1173K and 1373K by using a vacuum seal technique and the TG method. The dissociation pressure of oxygen for V_xW_1?xO₂ (0<x<1) was measured by using the EMF method at temperatures from 1173K to 1373K. The detailed phase diagram in the region, WWO₂VO₂V₂O₃, containing the complicated coexisting boundaries of the V_xW_1?xO₂ and V_nO_2n?1 (n:integer. ≥2) could be established at these temperatures. The standard Gibbs energy change of the formation of V_0.5W_0.5O₂ was calculated from the equilibrium partial pressure of oxygen.     

IR spectra of VO2 and V2O3

IR spectra of the tetragonal modification of VO₂ and of the trigonal form of V₂O₃ are recorded at room temperature and compared with that of V₂O₅. The investigated samples of the two lower-valent vanadium oxides, obtained on temperature-programmed reduction treatment, were also characterized with diffuse reflectance and electron-paramagnetic resonance spectra. The effect of atmospheric oxygen on these materials was revealed with XPS measurements and also studied with IR spectra.     

The system Ag2Se-Ho2Se3 in the 0-50 mol.% Ho2Se3 range and the crystal structure of two polymorphic forms of AgHoSe2

The phase diagram of the Ag₂Se-Ho₂Se₃ system in the range of 0-50 mol.% Ho₂Se₃ was constructed with the results of XRD and differential thermal analysis. A dimorphous compound exists in the system at the equimolar ratio of the components. The investigated part of the Ag₂Se-AgHoSe₂ diagram is of the eutectic type with the eutectic coordinates 7 mol.% Ho₂Se₃ and 1125 K. The crystal structure of the high-temperature modification of AgHoSe₂ was studied by X-ray powder diffraction method. α-AgHoSe₂ is described as a NaCl structure (space group ) with the lattice parameter а = 5.7623(3) Å. Atomic parameters were calculated in the isotropic approximation (R_I = 0.0434 and R_Р = 0.0636). The crystal structure of β-AgHoSe₂ was determined by X-ray structure analysis and was refined to R = 0.0487.     

Magnetic properties of (FexV1−x)V2S4 and (FexV1−x)V4S8

Magnetic properties of the systems (Fe_xV_1?x)V₂S₄ and (Fe_xV_1?x)V₄S₈ were studied by magnetic susceptibility and 57Fe Mössbauer effect measurements. In the case of (Fe_xV_1?x)V₂S₄, Nèel temperature (T_N) increases with increasing x. In contrast, T_N of (Fe_xV_1?x)V₄S₈ showed a decrease with increasing x. Mössbauer results showed that Fe in (Fe_xV_1?x)V₂S₄ is in a high spin state (magnetic), while Fe in (Fe_xV_1?x)V₄S₈ is in a low spin state (nonmagnetic).     

An ESR study of the heterogeneous system Cr2O3V2O5

An ESR study of the ‘products’ of the high temperature solid state reaction xCr₂O₃+yV₂O₅ ($\text{0.05≦(}\text{x}\text{y}\text{)≦2.0}$), aided by powder X-ray diffraction and IR spectra, has revealed (i) ‘unfamiliar’ paramagnetic intermediates Cr⁴⁺ and Cr⁵⁺, (ii) provided some clues to the oxidation of Cr³⁺ to Cr⁶⁺, and (iii) demonstrated a variety of exchange interactions involving V⁴⁺ and Cr³⁺.     

Phase relations in the CaAl2O4|CaGa2O4 system

The solid state reactions and the phase relations in the CaAl₂O₄|CaGa₂O₄ system, of which both end-members have the stuffed tridymite structure, were examined by using three kinds of starting materials; A (CaCO₃ + (Al,Ga)₂O₃), B (CaAl₂O₄ + CaGa₂O₄) and C (CaCO₃ + Al₂O₃ + Ga₂O₃). In the starting material B, a very low rate of solid state reaction between CaAl₂O₄ and CaGa₂O₄ was found, which seemed to be due to very slow interchange of Al³⁺ and Ga³⁺ located in tetrahedra of this structure. In order to obtain the probable equilibrium phase relations, it was necessary to use the starting material A. In the present system, a new phase was found in a wide range of composition as a stable phase, which was supposed to have the same structure as so-called metastable phase of CaGa₂O₄ and different array of tetrahedra from either CaAl₂O₄ or CaGa₂O₄|I.     

The system Eu2O3SrOV2O3 at 1400°C

Phase relations in a portion of the system Eu₂O₃SrOV₂O₃ have been investigated at 1400°C and a reduced pressure (10^?4mmHg). On heating, part of the trivalent vanadium was oxidized to the tetravalent state by atomospheric oxygen. The following ternary-phase solid solutions were identified: Eu_1?xSr_xVO_3?0.1x, SrO·2Eu_1?x?Sr_xVO_3?0.1x and SrO·Eu_1?xSr_xVO_3?0.1x.     

Topotactic redox reactions of the channel type chalcogenides Mo3S4 and Mo3Se4

Mo₃S₄ and Mo₃Se₄ were found to undergo topotactic electron-ion exchange reactions at ambient temperatures in aqueous and non-aqueous electrolytes containing transition or main group cations. The products of cathodic reduction are ternary phases A_xMo₃X₄. Mobilities of the exchangeable cations are rather high inside the solid and are responsible for high reaction rates. Cathodic reduction of Mo₃S₄ and Mo₃Se₄ represents a suitable method for the preparation of both stoichiometric and nonstoichiometric ternary phases which are of interest with respect to the superconducting properties of these chalcogenides.