Nonstoichiometry and defect structure of the perovskite-type oxides La1−xSrxFeO3−°

In order to elucidate the defect structure of the perovskite-type oxide solid solution La_1?xSr_xFeO_3?δ (x = 0.0, 0.1, 0.25, 0.4, and 0.6), the nonstoichiometry, δ, was measured as a function of oxygen partial pressure, P_O2, at temperatures up to 1200°C by means of the thermogravimetric method. Below 200°C and in an atmosphere of P_O2 ≥ 0.13 atm, δ in La_1?xSr_xFeO_3?δ was found to be close to 0. With decreasing log P_O2, δ increased and asymptotically reached $\text{x}\text{2}$. The value corresponding to $\text{δ =}\text{x}\text{2}$ was about ?10 at 1000°C. With further decrease in log P_O2, δ slightly increased. For LaFeO_3?δ, the observed δ values were as small as <0.015. It was found that the relation between δ and log P_O2 is interpreted on the basis of the defect equilibrium among Sr′_La (or V?_La for the case of LaFeO_3?δ), V^··_O, Fe′_Fe, and Fe^·_Fe. Calculations were made for the equilibrium constants K_ox of the reaction

$\text{1}\text{2}\text{O}{}_2\text{(g) + V}{}^{\mathrm{··}}{}_{\mathrm{o}}\text{+ 2Fe}{}^{\mathrm{x}}{}_{\mathrm{Fe}}\text{= O}{}^{\mathrm{x}}{}_{\mathrm{o}}\text{+ 2Fe}{}^{\mathrm{·}}{}_{\mathrm{Fe}}$

and K_i for the reaction

$\text{2Fe}{}^{\mathrm{x}}{}_{\mathrm{Fe}}\text{= Fe}{}^{\mathrm{\prime }}{}_{\mathrm{Fe}}\text{+ Fe}{}^{\mathrm{·}}{}_{\mathrm{Fe·}}$

Using these constants, the defect concentrations were calculated as functions of P_O2, temperature, and composition x. The present results are discussed with respect to previously reported results of conductivity measurements.     

Thermophysical properties of the intermetallic Mn3MN perovskites III. Heat capacity of the solid solution Mn3.2Ga0.8N

The heat capacity of the solid solution Mn_3.2Ga_0.8N was measured between 5 to 330 K by adiabatic calorimetry. A sharp anomaly with first-order character was detected at T_A = (160.5±0.5) K, corresponding to a magnetic rearrangement and a lattice expansion. No sharp anomaly was observed at T_c ≈ 260 K where the magnetic ordering takes place; instead, a smooth shoulder was detected. The thermodynamic functions at 298.15 K are $\text{C}{}_{\mathrm{<mtext>p,</mtext><mtext>m</mtext>}}\text{R}\text{= 15.16}$, $\text{S}{}_{\mathrm{m}}{}^{\mathrm{o}}\text{R}\text{= 18.57}$, $\text{{H}{}_{\mathrm{m}}{}^{\mathrm{o}}\text{(T)?H}{}_{\mathrm{m}}{}^{\mathrm{o}}\text{(0)}}\text{R}\text{= 2896}\text{K}$, $\text{?{G}{}_{\mathrm{m}}{}^{\mathrm{o}}\text{(T)?H}{}_{\mathrm{m}}{}^{\mathrm{o}}\text{(0)}}\text{RT}\text{= 8.85}$. At low temperatures the coefficient for the linear electronic contribution to the heat capacity was derived: γ = (0.031±0.003) J·K^?2·mol^?1. Moreover, the different contributions to the heat capacity were obtained and the electronic origin of the phase transitions was established.     

A theory of viscosity of dilute and moderately concentrated polymer solutions

A model theory of viscosity η for moderately concentrated polymer solutions is based on the assumption of a “local viscosity” effect and intermolecular hydrodynamic and thermodynamic interactions. It is shown that η is given by

$\text{η = η}{}_{\mathrm{o}}\text{{1 + γc[η]}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{·}\text{exp}\text{H}{}_{\mathrm{o}}\text{RT}\text{aø}\text{1 ? aø}$

where γ is 0–0.4 and depends on the quality of the solvent, a varies between 0,4 and 0.8 and depends on the fraction of the “free volume” of the systems, H₀ is the activation energy of the solvent and π is the polymer volume concentration. The dependence of η and “activation energy” of π and T for various molecular weights and qualities of solvents is described quantitatively. Anomalous dependences of [η] and of η on M for low polymer are obtained. An expression for η is proposed:

$\text{η}\text{η}{}_{\mathrm{o}}{}^{\mathrm{<mtext>1\; ?\; 2</mtext><mtext>K</mtext>}}\text{= {1 + (1 ? 2K)c[η]}F(π)}$

where K is the Huggins-Martin coefficient and F(π) = 1 for most solutions when T is > T_g. For poor solvents the H vs c curve (where H is the activation energy of η of solution) has a minimum value at moderate concentrations. For good solvents, H depends slightly on the molecular weight according to an empirical equation:

$\text{H = H}{}_{\mathrm{o}}\text{+}\text{660}\text{α}{}^3\text{1}\text{n}\text{η}\text{η}{}_{\mathrm{o}}$

Expressions are given from the viscosities of solutions of miscible and also solutions of immiscible polymers.     

Intramolecular relaxation of polystyrene in a theta solvent by photon-correlation spectroscopy

Photon-correlation spectroscopy has been used to measure the diffusion coefficient D and first-mode intramolecular relaxation time τ₁ of polystyrene in a theta solvent, cyclohexane at 34.5°C. Measurements were made on five narrow fractions ($\text{M}$_w = 2.88 × 10⁶ to 9.35 × 10⁶) as a function of concentration c, in the dilute regime. D varied linearly with c, D = D_o (I + k_Dc), with D_o = (1.4 ± 0.2) × 10^?4$\text{M}{}_{\mathrm{w}}{}^{\mathrm{?(0.508\pm 0.007)}}$ cm² s^?1. Although the values obtained for τ₁ were reproducible to within 5%, no systematic variation with c was detected. The results are fitted by the relation τ₁ = (7.7 ? 0.3) × 10^?8$\text{M}{}_{\mathrm{w}}{}^{\mathrm{(1.42\pm 0.05)}}$ μs, which agrees well with the theoretical expression of Zimm for the non-draining bead-and-spring model, modified for the light-scattering case.     

Synthesis of monohydridohexamethylbenzeneruthenium(II) complexes containing group V donor ligands. Isomerism arising from cyclometallation of a tertiary phosphine at aliphatic and aromatic carbon atoms

The η-hexamethylbenzenehydridoruthenium(II) complexes RuHCl(η-C₆Me₆)L (L = PPh₃ (11), AsPh₃ (12), P(C₆H₄-p-F)₃ (14), P(C₆H₄-p-Me)₃ (15), P(C₆H₄-p-OMe)₃ (16), P-t-BuPh₂ (17), P-i-PrPh₂ (18), P-i-Pr₃ (19), PCy₃ (20) and P-t-BuMe₂ (21)) have been made by heating [RuCl₂(η-C₆Me₆)]₂, the ligand and sodium carbonate in propan-2-ol. The triarylphosphine complexes 11, 14 and 15 react with methyllithium to give aryl ortho-metallated hydridoruthenium(II) complexes such as $\text{RuH(}\text{o}\text{-C}{}_6\text{H}{}_4\text{P}$Ph₂)(η-C₆Me₆) (22) and 19 similarly gives the isopropyl cyclometallated complex $\text{RuH(CH}{}_2\text{CHMeP}$-i-Pr₂(η-C₆Me₆) (29) as a mixture of diastereomers. Reaction of 17 with methyllithium gives initially the t-butyl cyclometallated complex $\text{RuH(CH}{}_2\text{CMe}{}_2\text{P}$Ph₂)(η-C₆Me₆) (25) which isomerizes by a first order process (k$\text{0}\text{?}$.2 h^?1 in C₆D₆ or THF-d₈ at 50°C) to the aryl ortho-metallated complex $\text{RuH(}\text{o}\text{-C}{}_6\text{H}{}_4\text{P}$-t-BuPh)(η-C₆Me₆) (26). The similarly generated isopropyl cyclometallated complex $\text{RuH(CH}{}_2\text{CHMeP}$Ph₂)(η-C₆Me₆) (27) has not been isolated in a pure state owing to rapid isomerization to $\text{RuH(}\text{o}\text{-C}{}_6\text{H}{}_4\text{P}$-i-PrPh)(η-C₆Me₆) (28); both 27 and 28 exist as a pair of diastereomers. The formation of the cyclometallated complexes and the isomerizations are thought to involve intermediate 16-electron ruthenium(O) complexes Ru(η-C₆Me₆)L.     

Valence state of the Fe ions in Sr1−yLayFeO3

The Sr²⁺_1?yLa³⁺_yFeO₃ system with 0.1 ≦ y ≦ 0.6 has been studied mainly by the Mössbauer effect. The results are discussed referring to the Ca_1?xSr_xFeO₃ system. The following four kinds of electronic phases have been observed: the paramagnetic and the antiferromagnetic average valence phases and the corresponding mixed valence phases. Two kinds of Fe ions coexist, in general, in the mixed valence phases. In the antiferromagnetic mixed valence phase, typically at 4 K, the magnetic hyperfine field and the center shift each takes a wide range of value depending on the composition, while a beautiful correlation is kept between them. The extreme values are close to those expected for Fe³⁺ and Fe⁵⁺. The appropriate chemical formulas are, therefore, Ca_1?xSr_xFe^(3+Δ)+_0.5Fe^(5?Δ)+_0.5O₃ and $\text{Sr}{}_{\mathrm{1?y}}\text{La}{}_{\mathrm{y}}\text{Fe}{}^{\mathrm{(3+\delta )+}}{}_{\mathrm{<mtext>(1+y)</mtext><mtext>2</mtext>}}\text{Fe}{}^{\mathrm{(5?\delta )+}}{}_{\mathrm{<mtext>(1?y)</mtext><mtext>2</mtext>}}\text{O}{}_3$.     

Synthesis of homoleptic tris(organo-chelate)iridium(III) complexes by spontaneous ortho-metallation of electronrich olefin-derived N,N′-diarylcarbene ligands and the X-ray structures of fac-[Ir{CN(C6H4Me-p) (CH2)2NC6H3Me-p}3] and mer-Ir{CN(C6H4Me-p)(CH2)2NC6H3Me-p}2 {CN(C6H4Me-p)(CH2)2NC6H4Me-p}Cl (a product of HCl cleavage)

Treatment of [{Ir(COD)(μ-Cl)}₂] with excess of the electron-rich olefin [$\text{CN(Ar)(CH}{}_2\text{)}{}_2\text{N}$Ar]₂ (abbreviated as (L^Ar)₂, Ar = C₆H₄Me-p or C₆H₄OMe-p) affords the ortho-metallated tricycle [$\text{Ir(L}{}^{\mathrm{A}}\text{r}$)₃], which for Ar = C₆H₄Me-p (Ia) with HCL yields [$\text{Ir(L}{}^{\mathrm{A}}\text{r}$)₂(L^Ar)]Cl (IV); X-ray data show that in IV there is an unexpectedly close Ir?C(o-aryl) contact (2;52(1) Å) involving the “free” L^Ar which compares with an IrC(o-aryl) distance of 2.09(3) Å in Ia or 2.07(3) Å in the ortho-metallated L^Ar ligand of complex IV.     

Mutual solubility of n-butanol + water under high pressures

The mutual solubilities of {xCH₃CH₂CH₂CH₂OH+(1-x)H₂O} have been determined over the temperature range 302.95 to 397.75 K at pressures up to 2450 atm. An increase in temperature and pressure results in a contraction of the immiscibility region. The results obtained for the critical solution properties are: T_o(U.C.S.T.) = 397.85 K and x_o = 0.110 at 1 atm; $\text{(}\text{dT}{}_{\mathrm{o}}\text{d}\text{p}\text{) = ?(12.0±0.5)×10}{}^{\mathrm{?3}}\text{K atm}{}^{\mathrm{?1}}$ at p < 400 atm and $\text{(}\text{dT}{}_{\mathrm{o}}\text{d}\text{p}\text{) = ?(7.0±0.7)×10}{}^{\mathrm{?3}}\text{K atm}{}^{\mathrm{?1}}$ at 800 atm < p < 2500 atm; $\text{(}\text{dx}{}_{\mathrm{o}}\text{d}\text{T}\text{) = ?(4.0±0.5)×10}{}^{\mathrm{?4}}\text{K}{}^{\mathrm{?1}}$.     

Détermination des modèles d'imperfections de différentes variétés allotropiques du sulfure cuivreux (digénite cubique,chalcocite hexagonale “haute et basse température”, chalcocite orthorhombique)

From the study of the CuCuBrCu_2?εSC solid cell in the range of cubic digenite and “high temperature” hexagonal chalcocite we have deduced the laws of variation of the deviation from stoichiometry and the holes concentration with the equilibrium partial pressure of sulfur (δ and p are found to be proportional to ). The electronic model corresponding to the formation of associations (V^×_CuV′_Cu) in the presence of neutral vacancies V^×_Cu allows one to explain these laws. In the low temperature range (range of “low temperature” hexagonal chalcocite and orthorhombic chalcocite) the study of thermal variations of Hall coefficient permits us to propose the following models: (a) the deviation from stoichiometry of the “low temperature” hexagonal chalcocite is due to the simple ionized vacancies V′_Cu; (b) the deviation from stoichiometry of the orthorhombic chalcocite is due to the vacancies V′_Cu and to the associations (V^×_CuV^×_Cu).     

Oxygen defect K2NiF4-type oxides: The compounds La2−xSrxCuO4−x2+δ

Oxygen defect K₂NiF₄-type oxides $\text{La}{}_{\mathrm{2?x}}\text{Sr}{}_{\mathrm{x}}\text{CuO}{}_{\mathrm{<mtext>4?</mtext><mtext>x</mtext><mtext>2</mtext><mtext>+\delta </mtext>}}$ have been synthesized for a wide composition range: 0 ≤ x ≤ 1.34. From the X-ray and electron diffraction study three domains have been characterized: orthorhombic compounds with La₂CuO₄ structure for 0 ≤ x < 0.10, tetragonal oxides similar to LaSrCuO₄ for 0.10 ≤ x < 1 and several superstructures derived from the tetragonal cell ( with n = 3, 4, 4.5, 5, 6) for 1 ≤ x ≤ 1.34. The compounds corresponding to 0 < x < 1 differ from the other oxides in that they are characterized by the presence of copper with two oxidation states: + 2 and + 3. A model structure for La_0.8Sr_1.2CuλO_3.4, in which copper has only the + 2 oxidation state, and for which the actual cell is tegragonal—a = 18.80₄ Å and c = 12.94 Å—has been established. The particular structural evolution of these compounds is discussed in terms of a competition between the capability of Cu(II) to be oxidized to Cu(III) and the ordering of oxygen vacancies.     

Proprietes magnétiques et étude par spectroscopie Mössbauer des tellurites de fer Fe2Te3O9 et Fe2Te4O11: Structure magnétique de Fe2Te4O11 à 4,2 K

Magnetic study and Mössbauer resonance measurements of the tellurites Fe₂Te₃O₉ and Fe₂Te₄O₁₁ characterize antiferromagnetic ordering. The transition temperatures determined by Mössbauer resonance, are 34 and 27 K, respectively. At 295 K the values of chemical shifts, 0.35 and 0.39 mm/sec, are typical of high-spin Fe(III) in octahedral coordination. Neutron powder diffraction was used to determine the magnetic structure of Fe₂Te₄O₁₁ at 4.2 K. It shows antiferromagnetic interactions between Fe³⁺ ions belonging to [Fe₂O₁₀] groups. The magnetic space group is $\text{P}{}_{\mathrm{2a}}\text{2}{}_1\text{c}$.     

Dilute and concentrated solutions of polystyrene in trans-decalin close to and far from the θ-temperature—II. Osmotic pressure measurements

Osmotic pressure measurements on polystyrene ($\text{M}{}_{\mathrm{n}}\text{= 396. 000}$) in trans-decalin for concentrations up to 140 kg m^?3 and from 20 to 40 are reported. The θ-temperature is 20.8 . The ratio

where c⁺ is the concentration at which a homogeneous segment distribution is assumed to prevail, increases with temperature up to the plateau value of 0.7. From the temperature dependence of the osmotic pressure, the partial molar enthalpy. Δh₁, and entropy, Δs₁. of mixing are found to be positive. The solvent-solute interaction parameter increases linearly with concentration at all temperatures.     

Etude de la structure K2NiF4 par la méthode des invariants,I. Cas des oxydes A2BO4

The study of the K₂NiF₄ structure by the “method of invariants” leads to the relationship

$\text{0.99615 V}\text{1}\text{3}\text{=β}{}_{\mathrm{B}}\text{+ψ}{}_{\mathrm{A}}\text{2}\text{1}\text{2}$

with V = a²c (β_B and ψ_A are invariant values associated with cations B and A) in compounds with K₂NiF₄ structures. Some values of ψ_A and examples are proposed.     

A dynamic nuclear magnetic resonance study of 1,3-intramolecular shifts in pentacarbonyl-chromium(O) and -tungsten(O) complexes of β-2,4,6-trimethyl-1,3,5-trithian, 1,3,5-trithian, 1,3-dithian and 2-methyl-1,3-dithian: the x-ray crystal structure of [W(CO)5{SCH(Me)SCH(Me)SCH(Me)}]

Variable temperature ¹H NMR spectroscopy has been used in the study of 1,3-intramolecular shifts of the M(CO)₅ moiety in complexes of the general formula [M(CO)₅L], (M = Cr or w), L = $\text{SCH}{}_2\text{SCH}{}_2\text{SC}$H₂, $\text{SCH}{}_2\text{SCH}{}_2\text{CH}{}_2\text{C}$H₂ and $\text{SCH(Me)SCH}{}_2\text{CH}{}_2\text{C}$H₂. For the 1,3,5-trithian complexes precise energy barriers for the process have been obtained by detailed computer simulation of the static and dynamic spectra. Our results suggest that the magnitude of ΔG^≠ (298.15 K) for the 1,3-shift is largely dependent upon the skeletal flexibility of the ligand system. In this context we have investigated the X-ray crystal structure of the highly substituted trithian complex [W(CO)₅{β-$\text{SCH(Me)SCH(Me)SC}$H(Me)}].     

Etude comparative des structures type K4NiF4 et pérovskite par la méthode des invariants

The study of K₂NiF₄ and perovskite structure type by the “method of invariants” leads to the relationship: $\text{(A-X)}{}_9\text{2}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{? (A-X)}{}_{12}\text{=}\text{constant}$, where (A-X)₉ and (A-X)₁₂ are the invariant values associated with cation A in coordination number 9 and 12. In the case where A = K⁺ and X = F^?, we propose the relationship:

$\text{(K}{}^{\mathrm{+}}\text{?F)}{}_{\mathrm{R}}\text{= 2.832 R}{}^{\mathrm{<mtext>1</mtext><mtext>11.4</mtext>}}$

where R is the coordination number.     

Etude par diffraction de neutrons de la phase Sr0,5La1,5Li0,5Fe0,5O4

A neutron diffraction study has been carried out on Sr_0.5La_1.5Li_0.5Fe_0.5O₄ of K₂NiF₄-type derived structure and it has shown that iron in the tetravalent state has a high spin configuration (t³_2ge¹_g) and that the material has some stacking defects. At room temperature this compound shows an ordering between iron and lithium atoms leading to a nuclear cell a₀√2, a₀√2, c₀ (a₀ and c₀ are the parameters of the K₂NiF₄-type cell). At low temperature ($\text{T <}\text{T}{}_{\mathrm{<mtext>N</mtext>}}\text{2}$) the magnetic structure can be described as antiferromagnetic, corresponding likely to a colinear pattern with a propagation vector of 0.5 ($\text{2π}\text{a}{}_0$) along the [110] axis. At higher temperature ($\text{T}{}_{\mathrm{<mtext>N</mtext>}}\text{2}\text{< T < T}{}_{\mathrm{<mtext>N</mtext>}}$) helimagnetic structure is consistent with a propagation vector of 0.47 ($\text{2π}\text{a}{}_0$) [110].     

Heat capacity and thermodynamic functions of CsCrCl3 and RbCrCl3. Structural phase transitions

We present the heat capacities measured by adiabatic calorimetry from 6 to 350 K, and by differential scanning calorimetry from 300 to 500 K, of CsCrCl₃ and RbCrCl₃. A first-order transition at T_c = (171.1±0.1) K was detected for CsCrCl₃. The RbCrCl₃ showed at T_c = (193.3±0.1) K a transition with thermal hysteresis at temperatures just below the maximum. At T₁ = (440±10) K a continuous transition was also detected. Furthermore, at T_N ≈ 16 K, and for both compounds, a small bump due to magnetic long-range ordering was observed. The thermodynamic functions at 298.15 K are

     

19.

Optical and structural investigation of the lanthanum β-alumina phase doped with europium     

J. Dexpert-Ghys  M. Faucher  P. Caro 《Journal of solid state chemistry》1976,19(2):193-204

The lanthanum β-alumina phase doped with europium was investigated by X-ray diffraction and fluorescence. This nonstoichiometric phase exists over the composition range: $\text{11}\text{Al}{}_2\text{O}{}_3\text{1}\text{La}{}_2\text{O}{}_3$ to $\text{14}\text{Al}{}_2\text{O}{}_3\text{1}\text{La}{}_2\text{O}{}_3$. The unit cell is hexagonal hexagonal with a = 5.560 ± 0.003 Å, c = 22.001 ± 0.003 Å and belongs to the $\text{P6}{}_3\text{mmc}$ space group. X-ray diffraction patterns do not vary between both boundary compositions, but fluorescence spectra show that the structure of the mirror plane in which the lanthanide ions are located is deeply modified. The atomic structure of the mirror plane is of “β-type” (like β(Na) or β(Ag)) for the lower alumina contents; it gradually changes to a “magnetoplumbite type” for higher alumina contents.     

20.

Gibbs energy of formation of cobalt divanadium tetroxide     

K.T. Jacob  S.Shashidhara Pandit 《Journal of solid state chemistry》1985,60(2):237-243

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.     

	$\text{C}{}_{\mathrm{<mtext>p,</mtext><mtext>m</mtext>}}\text{R}$	$\text{S}{}_{\mathrm{m}}{}^{\mathrm{o}}\text{R}$	$\text{{H}{}_{\mathrm{m}}{}^{\mathrm{o}}\text{(T)?H}{}_{\mathrm{m}}{}^{\mathrm{o}}\text{(0)}}\text{R}\text{K}$	$\text{?{G}{}_{\mathrm{m}}{}^{\mathrm{o}}\text{(T)?H}{}_{\mathrm{m}}{}^{\mathrm{o}}\text{(0}}\text{RT}$
CsCrCl3	15.38	26.49	3503.2	14.735
RbCrCl3	15.76	25.99	3556.8	14.384

Optical and structural investigation of the lanthanum β-alumina phase doped with europium

The lanthanum β-alumina phase doped with europium was investigated by X-ray diffraction and fluorescence. This nonstoichiometric phase exists over the composition range: $\text{11}\text{Al}{}_2\text{O}{}_3\text{1}\text{La}{}_2\text{O}{}_3$ to $\text{14}\text{Al}{}_2\text{O}{}_3\text{1}\text{La}{}_2\text{O}{}_3$. The unit cell is hexagonal hexagonal with a = 5.560 ± 0.003 Å, c = 22.001 ± 0.003 Å and belongs to the $\text{P6}{}_3\text{mmc}$ space group. X-ray diffraction patterns do not vary between both boundary compositions, but fluorescence spectra show that the structure of the mirror plane in which the lanthanide ions are located is deeply modified. The atomic structure of the mirror plane is of “β-type” (like β(Na) or β(Ag)) for the lower alumina contents; it gradually changes to a “magnetoplumbite type” for higher alumina contents.     

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.