Phase diagram and some physical properties of V2O3+x1 (0 ? x ? 0.080)

The magnetic and electric properties of V₂O_3+x were investigated by measurements of magnetic susceptibility, electrical resistivity, magnetotorque, Mössbauer of doped ⁵⁷Fe, and NMR of ⁵¹V, and the results were compared with those of the (V_1?xTi_x)₂O₃ system or highly pressured V₂O₃. The results obtained are as follows: (1) The metallic state shows an antiferromagnetic ordering at T_N (x). The value of T_N for metallic V₂O₃, obtained by interpolation to x = 0, shows the coincidence between V₂O_3+x and the (V_1?xTi_x)₂O₃ system. (2) Magnetic susceptibility of V₂O_3+x is expressed as χ_M(V₂O_3+x) = (1?x)χ_M(V³⁺) + xχ_M(V⁴⁺). χ_M(V⁴⁺) obeys the Curie-Weiss law $\text{(χ}{}_{\mathrm{<mtext>M</mtext>}}\text{(}\text{V}{}^{\mathrm{4+}}\text{) =}\text{0.77}\text{T}\text{+ 17)}$. (3) In the insulating phase, the electrical resistivity ? is expressed as a common equation: $\text{? = 10}{}^{\mathrm{?1.8}}\text{exp}\text{(}\text{E}\text{kT}\text{)}$. This implies that the substitution of Ti or nonstoichiometry (V⁺⁴ + metal vacancies) has little influence on the carrier mobility (or bandwidth). (4) There is a critical length in the c-axis (? 14.01 Å) where the metal-insulator transition takes place. This suggests that the length of the c-axis plays an important role in the metal-insulator transition of V₂O₃-related compounds.     

The crystal structure of a metastable binary phase related to β-Ga: β′-Ga(In)

A metastable GaIn phase with 9–12 at.% In has been prepared by rapid quenching (splat cooling) to ～ 80°K. The structure of this phase was found to be orthorhombic, α-U type, Cmcm, a₀ = 2.770 ± 1Å, b₀ = 8.183 ± 4Å, c₀ = 3.306 ± 2Å, $\text{V}\text{atom}\text{18.73 ± 2}$ų (at 10 at.% In and ～ 80°K), with disordered Ga_1?xIn_x atoms in position 4(c) with y = 0.127 ± 4. β′-Ga(In) is structurally closely related to monoclinic β-Ga, and it can be considered as a distorted metastable binary extension of β-Ga.     

The crystal and molecular structure of tris[(triphenylstannyl)methyl]methane

The title compound, C₅₈H₅₂Sn₃, belongs to the triclinic space group P$\text{1}$, with a 10.165, b 13.365, c 18.670 Å, α 96.28, β 93.88, γ 103.15°, V = 2443.8 ų, f_w = 1105.1, Z = 2, D_calc 1.501 g cm^?3, m.p. 206.5–208°C, λ(Mo-K_$\text{α}$) 0.71069 Å. The structure was refined on 2684 nonzero reflections to an R factor of 0.044. The crystal contains molecules in which the (SnCH₂)₃CH core possesses an approximate C₃ symmetry. The three SnC(H₂) bonds are gauche to the C(4)-H bond. Repulsive interactions involving the bulky Ph₃Sn substituents lead to large SnC(H₂)C(H) angles (av. 117.3°), whereas the C(H₂)C(H)C(H₂) angles at the tertiary carbon average 111.3°. Little distortion of the Ph₃Sn groups themselves is present, since the PhSnPh angles (av. 109.8°) are almost equal to the C(H₂)SnPh angles (av. 109.9°). The molecule as a whole has no symmetry because the aromatic rings in the three Ph₃Sn groups have different orientations. The phenyl groups create a pocket in the middle of the molecule which encloses and shields the tertiary hydrogen atom. The resulting inaccessibility of this hydrogen accounts in part for the low reactivity of the title compound in redox reactions.     

Röntgenographische,thermoelektrische, und IR-spektroskopische Untersuchung des Spinellsystems LixMn1−xV2O4

The spinels of the system Li_xMn_1?xV₂O₄ (0 ? x ? 1) have been prepared at 700–750°C from LiV₂O₄ and MnV₂O₄. The lattice constants decrease linearly with increasing x. In the region x>0.75, the d-electrons of V should be delocalized as the VV distances are lower than the critical VV separation of 2.94 Å. Experimentally, the samples with x>0.6 show no IR absorption bands and the Seebeck coefficient is near zero. The Seebeck coefficient can be described with a model of intermediate polarons and can be expressed by the equation $\text{Θ = 198}\text{log}\text{[1 +}\text{(1 ? x)}{}^5\text{x}\text{]}$.     

Estimation of the standard entropy change on complete reduction of oxide MmOn

The standard entropy change ΔS° for the reduction of nonmagnetic, nonconducting oxides, $\text{M}{}_{\mathrm{m}}\text{O}{}_{\mathrm{n}}\text{(}\text{s}\text{) = mM(}\text{s}\text{) + (}\text{n}\text{2}\text{)}\text{O}{}_2\text{(g)}$, has been estimated as a function of m, n, and temperature T from motional entropies of oxygen molecules and vibrational entropies of solid phases. An available formula of ΔS°_calc = a · m + b · n with constant a and b based on effective Debye temperatures, θ_M = 165 K for M and θ_OX = 540 K for M_mO_n, agrees well with the observed ΔS°_obs for M₂O, MO, M₂O₃, MO₂, M₂O₅, and MO₃ in the temperature range T = 300 – 1300 K. Possible electronic entropy corrections are applied to ΔS°_calc for M₂O₇ and MO₄.     

Phase equilibria and thermodynamics of coexisting phases in rare-earth element-iron-oxygen systems. II. The praseodymium-iron-oxygen system

The phase equilibria and the thermodynamics of coexisting phases in the PrFeO system have been studied using static and dynamic methods for attaining equilibrium with subsequent annealing and identification of the condensed phases by X-ray analysis. Equilibrium phase diagrams have been constructed to define the changes that take place in the PrFeO system on variation of the partial oxygen pressure, the temperature, and the composition of the initial mixture of oxides. An isothermal cross section at 1300°K and equilibrium diagrams of the type P_O2 = f(composition) with with one composition parameter fixed and T = f(composition) with P_O2 = constant have been constructed. It has been shown in the PrFeO system that only one ternary compound with perovskite structure, PrFeO₃, is formed, and furthermore, it is stable no matter how high the partial oxygen pressure.     

Untersuchung der magnetischen Suszeptibilität zum Studium des Bindungsverhaltens von Eisen in V1−xFexO2−xFx

An analysis of the magnetic susceptibility of V_1?xFe_xO_2?xF_x with 0.0026 ? x ? 0.015 in the semiconducting M₁-phase yields a magnetic moment of 5.03 μ per Fe³⁺ ion. Deviations from the Curie-Weiss behavior above T = 120°K are due to the existence of current carriers n, in the V⁴⁺-conduction band. The very high effective mass ($\text{m}{}_{\mathrm{<mtext>e</mtext>}}\text{? 100 m}{}_0$) of the carriers can be explained by the spin polarization cloud which they carry along. A comparison between the activation energy determined from the average slope of the log n vs T^?1 curve and from electric conductivity measurements implies an activated hopping mobility of the charge carriers.This hopping mobility is due to the onset of the Anderson localization resulting from disorder which is induced by the foreign (Fe³⁺, F^?)-ions. Mössbauer-spectroscopic measurements also confirm a reduction of the localized 3d-electrons of the Fe³⁺-cation in V_1?xFe_xO_2?xF_x above T = 120°K.     

Phase equilibria in the system V2O3Ti2O3TiO2 at 1473°K

The phase equilibria in the V₂O₃Ti₂O₃TiO₂ system have been determined at 1473°K by the quench method, using both sealed tubes and controlled gaseous buffers. For the latter, $\text{CO}{}_2\text{H}{}_2$ mixtures were used to vary the oxygen fugacity between 10^?10.50 and 10^?16.73 atm. Under these conditions the equilibrium phases are: a sesquioxide solid solution between V₂O₃ and Ti₂O₃ with complete solid solubility and an upper stoichiometry limit of (V, Ti)₂O_3.02; an M₃O₅ series which has the V₃O₅ type structure between V₂TiO₅ and V_0.69Ti_2.31O₅ and the monoclinic pseudobrookite structure between V_0.42Ti_2.58O₅ and Ti₃O₅; series of Magneli phases, V₂Ti_n?2O_2n?1Ti_nO_2n?1, n = 4–8; and reduced rutile phases (V, Ti)O_2?x, where the lower limit for x is a function of the $\text{V}\text{(V + Ti)}$ ratio. The extent of the different solid solution areas and the location of the oxygen isobars have been determined.     

Nouveau diagramme de phase pour le système (1 − x)V2O5 · xPbO dans le domaine x < 23

Phase diagram of the system (1 − x)V₂O₅ · xPbO is revised in the rich V₂O₅ region (x < 0.66). Two new eutectic compositions are evidenced: x = 0.4975 (15) (T_E1 = 478°C) and x = 0.5035 (15) (T_E2 = 480°C). Some melting points are also refined.     

Isothermal decomposition of ternary oxide AxByOz on an isobar—Stability of perovskite ABO3 (A = La,Sm, Dy; B = Mn,Fe) in a reducing atmosphere

The isothermal decomposition of any ternary oxide A_xB_yO_z on liberation of n moles of oxygen at a constant pressure is found to be driven by the mixing entropy ΔS_m = ?nRln P_O2 of the total entropy change ΔS = ΔS° + ΔS_m. The stability of A_xB_yO_z towards isothermal decomposition into a biphasic solid mixture is derived from the equilibrium condition $\text{ΔG1 = 0}$ as functions of standard changes ΔH° and ΔS°. Assuming ΔS° = 44n and calculating ΔH° in terms of lattice energies U(ABO₃) and U(A₂O₃), the stability of perovskites is given as a function of the ionic radius of the A³⁺ ion. The calculated stability agrees well with that observed. The effect of electronic entropy change ΔS_e on ΔS° is demonstrated for AFeO₃ (A = La, Sm, Dy).     

Thermodynamic study of nonstoichiometric tungsten trioxide WO3−x by EMF measurements at high temperature

The values of ΔG(O₂), ΔH(O₂), and ΔS(O₂) have been determined from electrochemical cell measurements, within the whole homogeneity range of WO_3?x, between 700 and 900°C. The samples have been previously prepared by equilibration of WO₃ pellets with COCO₂ mixtures and their composition has been determined by thermogravimetry. A single phase has been found between WO₃ and WO_2.9760. The results may be understood by considering a structure involving point defects, singly ionized oxygen vacancies V^·_O between WO₃ and WO_2.9880. For larger departure from stoichiometry, the variations of ΔH(O₂) and ΔS(O₂) suggest the formation of more complex defects. The enthalpy of formation of V^·_O has been calculated: 78 kcal · mole^?1.     

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.     

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.     

The crystal structure of Cs[VOF3] · 12H2O

The crystal structure of $\text{Cs[VOF}{}_3\text{]}\text{·}\text{1}\text{2}\text{H}{}_2\text{O}$ has been determined and refined on the basis of three-dimensional X-ray diffractometer data (MoKα radiation). The structure is monoclinic, a = 7.710(2), b = 19.474(7), c = 7.216(2)Å, β = 116.75(1)°, V = 967.5ų, Z =8, space group Cc (No. 9). The final R and R_w were 0.0295 and 0.0300, respectively, for 1356 independent reflections and 117 variables.The structure contains two crystallographically different VOF₅ octahedra linked so as to form complex chains. Two non-equivalent octahedra share one FF edge, forming V₂O₂F₈ doublets. Two F atoms, connected to different V atoms within the doublet, form an edge in the adjacent equivalent V₂O₂F₈ unit thus continuing the chain. The VO distances are 1.583(7) and 1.595(7) Å. The VF distances are in the range 1.881-2.205 Å, mean value: 1.989 Å. The H₂O group is a crystal water molecule.     

Phase equilibria and thermodynamics of coexisting phases in rare-earth element-iron-oxygen systems. I. The cerium-iron-oxygen system

In the present work it is shown that in the CeFeO system only one ternary compound with a perovskite structure, the orthoferrite CeFeO₃, is formed. We define the crystallographic properties of cerium ferroperovskite more accurately. The thermodynamics of its oxidation and reduction over a temperature range of 900–1200°C are studied using the emf method with a solid electrolyte.It is shown that the free energy of cerium orthoferrite formation from the oxides according to the reaction $\text{1}\text{2}\text{Ce}{}_2\text{O}{}_3\text{+}\text{1}\text{2}\text{Fe}{}_2\text{O}{}_3\text{=}\text{CeFeO}{}_3$, derived from data on the equilibrium oxidation of CeFeO₃, differs very little from the value of ΔG°, calculated from the magnitude of the equilibrium pressure of oxygen over the orthoferrite and reduction products coexisting with it.Phase equilibria and the thermodynamics of coexisting phases in the CeFeO system have been investigated. Equilibrium diagrams are constructed which define the character of the changes taking place in the CeFeO system during changes in partial oxygen pressure, temperature, and composition of the initial oxide mixture. Thus, we have equilibrium diagrams of the type P_O2 = f(composition) with T = constant; with one composition parameter fixed; and T = f(composition) with P_O2 = constant.     

Magnetic investigation of Er(C2O4) (C2O4)·3H2O

Single crystal susceptibilities of Er(C₂O₄) (C₂O₄H)·3H₂O are reported over the 1.5–20 K interval, and EPR spectra at 4.2 K of Y (C₂O₄) (C₂O₄H·3H₂O doped with Er³⁺ are also reported. The susceptibilities follow the CurieWeiss law, with g_| = 12.97 ± 0.05, g_⊥ = 2.98 ± 0.05, θ_| = ?0.25 ± 0.05 K, and θ_⊥ = ?0.12 ± 0.05 K.     

Synthesis and study of high-temperature heat capacity of erbium orthovanadate

Orthovanadate ErVO₄ has been prepared by solid-phase synthesis from a stoichiometric mixture of high pure V₂O₅ and chemically pure Er₂O₃ by multistage calcination in air in the temperature range 873–1273 K. The effect of temperature (380–1000 K) on the heat capacity of orthovanadate ErVO₄ was studied by hightemperature calorimetry. Thermodynamic properties of erbium orthovanadate (enthalpy change H°(T)–H°(380 K), entropy change S°(T)–S°(380 K), and reduced Gibbs energy Φ°(T)) have been calculated from the experimental C_p = f(T) data. It has been shown that the specific heat varies in a row of oxides and orthovanadates of Gd-Lu naturally depending on the radius of the R³⁺ ion within the third and fourth tetrads.     

The crystal structures of Ti2O3, a semiconductor,and (Ti0.900V0.100)2O3, a semimetal

The crystal structures of the semiconductor Ti₂O₃ and the semimetal (Ti_0.900V_0.100)₂O₃ were determined from X-ray diffraction data collected from single crystals. The compounds are isostructural with Al₂O₃ of rhombohedral unit cell dimensions of a = 5.4325(8) Å and α = 56.75(1)° for Ti₂O₃, and a = 5.4692(8) Å and α = 55.63(1)° for the doped system. The effect of substitution of V⁺³ is to increase the metal-metal distance across the shared octahedral face from 2.579 Å in Ti₂O₃ to 2.658 Å in (Ti_0.900V_0.100)₂O₃, while decreasing the metal-metal distance across the shared octahedral edge from 2.997 to 2.968 Å. The metal-oxygen distances exhibit only small changes. These structural changes are consistent with the band theory proposed by Van Zandt, Honig, and Goodenough (9) to explain changes in electrical and other properties with increasing vanadium content in (Ti_1?xV_x)₂O₃.     

Gibbs energy of formation of cobalt divanadium tetroxide

The Gibbs energy of formation of V₂O₃-saturated spinel CoV₂O₄ has been measured in the temperature range 900–1700 K using a solid state galvanic cell, which can be represented as $\text{Pt, Co + CoV}{}_2\text{O}{}_4\text{+}\text{V}{}_2\text{O}{}_3\text{(CaO)}\text{ZrO}{}_2\text{Co}\text{+}\text{CoO, Pt}$. The standard free energy of formation of cobalt vanadite from component oxides can be represented as CoO (rs) + V₂O₃ (cor) → CoV₂O₄ (sp), ΔG° = ?30,125 ? 5.06T (± 150) J mole^?1. Cation mixing on crystallographically nonequivalent sites of the spinel is responsible for the decrease in free energy with increasing temperature. A correlation between “second law” entropies of formation of cubic 2–3 spinels from component oxides with rock salt and corundum structures and cation distribution is presented. Based on the information obtained in this study and trends in the stability of aluminate and chromite spinels, it can be deduced that copper vanadite is unstable.