Dissociation pressure and Gibbs energy of formation of Y3Fe5O12 and YFeO3

Compounds in the ternary system Y  Fe  O are of significant interest due to their magnetic properties. Electrochemical solid state galvanic cell techniques have been employed to study their thermodynamic properties in the temperature range from 900 to 1250 °C. The following oxygen dissociation pressures were obtained: log P_O2$\text{[}\text{Pa}\text{] = ?}\text{26365}\text{T}\text{+ 17.13}$ for yttrium iron garnet, Y₃Fe₅O₁₂, in the entire temperature range, log P_O2$\text{[}\text{Pa}\text{] = ?}\text{29345}\text{T}\text{+ 13.00}$ for perovskite, YFeO₃, below 1080 °C and log P_O2$\text{[}\text{Pa}\text{] = ?}\text{39375}\text{T}\text{+ 20.43}$ for YFeO₃ above 1080 °C. The standard Gibbs energies of formation from metallic iron, yttria (Y₂O₃) and oxygen were determined to be $\text{2}\text{G}{}^{\mathrm{o}}\text{= ? 2078.2 + 0.5850·}\text{T kJ}\text{/}\text{mol}$ for the formation of Y₃Fe₅O₁₂ and $\text{2}\text{G}{}^{\mathrm{o}}\text{= ? 421.3 + 0.1148·}\text{T kJ}\text{/}\text{mol}$ for the formation of YFeO₃. The standard enthalpies and entropies of formation are ? 2078.2 kJ/mol and ? 585.0 J/mol·K for Y₃Fe₅O₁₂ and ? 421.3 kJ/mol and ? 114.8 J/mol·K for YFeO₃, respectively.     

Metal-ion distribution and magnetic structure of Fe-substituted cobaltite spinel: FeCo2O4

The metal ion distribution of FeCo₂O₄ (cubic spinel) which was quenched from 900°C in air was determined to be ($\text{Fe}$³⁺_0.18$\text{Co}$²⁺_0.82) [$\text{Fe}$³⁺_0.82$\text{Co}$²⁺_0.18 Co^III+_1.0] O₄ with the neutron diffraction method. The oxygen spacial parameter u was determined to be 0.382 ± 0.002. The magnetic structure was explained as a Néel type ferrimagnet and the origin of the spontaneous magnetization was attributed to the uncompensation of the spins between A- and B-site of the spinel lattice. The magnetic moment per molecule was estimated to be 0.70 μB.     

Interactions magnetiques hyperfines et quadrupolaires combinees pour les ions d'impuretes 119Sn2+ dans Cr2O3

Hyperfine magnetic interactions have been observed for the first time for Sn²⁺ ions introduced as doping agents in a magnetically ordered oxide (¹¹⁹Sn: Cr₂O₃). Mössbauer resonance at low temperature shows for ¹¹⁹Sn²⁺ the simultaneous presence of hyperfine magnetic and quadrupole interactions, which have the same order of magnitude at 77 K. From the spectra, the following parameters have been determined: tranfered hyperfine magnetic field: H_Sn²⁺ (77 K = 38 ± 1kOe, sign and value of the quadrupole interaction constant: eV_zzQ = + 3,6 ± 0,3 mm/s, asymmetry parameter: η = 0,15 ± 0,05, polar (θ) and azimutal (?) angles: $\text{θ ? ? ? 90°}$, and chemical shift: $\text{δ}\text{BaSnO}{}_3\text{= + 2,89 ± 0,02}\text{mm}\text{/}\text{s}$. The investigation shows that Sn²⁺ is localized at the surface of the Cr₂O₃ grains.     

Preparation et caracterisation des ferrites de calcium CaFe2+nO4+n a valeurs fractionnaires de n (32, 52) et leur incidence sur le diagramme Fe-Ca-O A 1120°C

The synthesis of two new calcium ferrites belonging to the CaFe_2+nO_4+n family, with the fractional values $\text{n =}\text{3}\text{2}$ and $\text{5}\text{2}$, has been done.Their crystalline structures have been determined. A stacking process of blocks with the CaFe₂O₄ composition and blocks with the FeO composition, like for the other terms of the series with n integer (1, 2, 3) allows to describe them.The schematic representation of this new example of intergrowth has been carried out according to A.F. Wells' method.The existence of these ferrites has lead us to specify the Fe-Ca-O diagram at 1120°C in the FeO-Ca₂Fe₂O₅-CaFe₂O₄ - Fe₃O₄ region.     

Temperature dependence of the growth-induced anisotropy of Ge-substituted garnet films by resonance techniques

Ferromagnetic resonance techniques have been used to measure the growth-and stress-induced uniaxial magnetic anisotropy of LPE grown garnet films of the nominal composition Y_1.64Eu_0.10Lu_0.30Ca_0.96Ge_0.96Fe_4.04O₁₂ from 130°K to near the Curie temperature, 455°K. The longitudinal and transverse resonance fields were measured prior and subsequent to an anneal at 1453°K. The growth-induced anisotropy, K^G_u ～?0.03 × 10⁴ ergs/cm³ at 300°K, was found to be approximately 10% of the stress-induced anisotropy, and of opposite sign for these tensile films. The associated anisotropy field, $\text{2}\text{K}{}^{\mathrm{G}}{}_{\mathrm{u}}\text{M}$ exhibited a reversal of slope, with a maximum occurring at 310°K. A model which assumes the existence of a surface anisotropy is proposed to explain these observations. The temperature dependence of the cubic anisotropy, the magnetization, the linewidth, and the exchange constant have been measured also.     

Crystal growth and magnetic properties of NdFeTiO5

Single crystals of NdFeTiO₅ have been grown for the first time by using the flux technique. The observed X-ray reflections were compatible with the space group Pbam and the lattice parameters deduced from both single crystal rotation photographs and powder diffraction patterns are $\text{a}\text{= 7.500}\text{A}\text{?}$, $\text{b}\text{= 8.746}\text{A}\text{?}$ and $\text{c}\text{= 5.847}\text{A}\text{?}$. The crystals were found to undergo a magnetic transition to an antiferromagnetic state at T_N = 18.5 ± 0.5 K. The calculated temperature dependence of the Fe³⁺ and Nd³⁺ sublattice magnetizations based on the results of magnetic susceptibility measurements is presented.     

High temperature superconductivity in the LiTiO ternary system

The first high temperature superconducting oxide compound is reported. The compound is Li_1+xTi_2?xO₄ and has the face-centered cubic spinel structure, with $\text{a}{}_{\mathrm{o}}\text{? 8.40}\text{A}\text{?}$. The transition temperatures of this compound range from ～ 7°K to 13.7°K.     

Proprietes magnetiques de l'oxyde de vanadium V3O7

Magnetic susceptibility and magnetization measurements on V₃O₇ from 4,2 to 600 K characterize a paramagnetic behaviour above 18 K : the samples follow a Curie-Weiss law with a Curie constant in good agreement with a spin only value $\text{S}\text{=}\text{1}\text{2}$ per V⁴⁺. At lower temperature the magnetic ordering may be attributed to a metamagnetic behaviour resulting from the layer type structure.     

Oxidation-reduction reactions of CeMO4+x (M = Ta or Nb) phases

Phase equilibrium methods, single crystal and powder x-ray diffraction analyses, thermogravimetric analysis and magnetic susceptibility measurements were utilized to define subsolidus phase relations $\text{in air}$ for the systems cerium oxide - Ta₂O₅ and cerium oxide - Nb₂O₅. Stoichiometric CeTaO₄ is stable in air (P_O2 = 0.21 atm) only above 1265°C. At 1265°C, the reversible reaction, $\text{3}\text{CeTaO}{}_4\text{+}\text{1}\text{2}\text{?}$CeTa₃O₉ + 2CeO₂ is established. If CeTaO₄ is quenched to room temperature and $\text{reheated}$ below 1000°C, or, if the material is rapidly cooled from above 1265°C to below 1000°C it absorbs oxygen according to, . The x parameter is variable and temperature dependent. Using a thermal microbalance, three distinct complex reaction series involving a homogeneity range in x were established, (a) 0.50 ≥ × ≥ 0.48 (<350°–600°C), (b) 0.17 ≥ × ≥ 0.06 (600°–950°C), (c) 0.40 ≥ × ≥ 0.34 (950°-room temperature). CeNbO₄ (not isostructural with CeTaO₄) also absorbs oxygen below ≈700°C in air to yield CeNbO_4+x materials.     

Crystal structure of K4[H2J2O10].8H20

Crystals of K₄ [H₂J₂O₁₀] 8H₂O belong to the triclinic system, space group P 1 with a = 7.161 (2) $\text{A}\text{?}\text{, b}\text{= 10,553}$ (5) $\text{A}\text{?}\text{, c}\text{= 7,081}$ (2) $\text{A}\text{?}\text{, α = 98°1′}$, β = 117°8′, γ = 90°6′ and Z = 1. The crystal structure has been determined on the basis of photographic data from 877 independent reflections, with the final R value of 6,6%. The iodine atoms are surrounded by a distorted octahedra consisting of five oxygen atoms and one OH group. The average J-O distance is 2.03 Å. There are 2 independent K atoms in the structure. K(1) has a coordination number of eight, while K(2) is surrounded by 6 (5 water molecules + one OH group) nearest neighbours.     

Magnetic and crystallographic properties of Fe1−x(Cu0.5In0.5)xCr2S4 spinels

Fe_1?x(Cu_0.5In_0.5)_xCr₂S₄ spinel powders with 0 ≤ x ≤ 1 were prepared. Their lattice constant (a_o) increases linearly with x from a_o = 0.9995 nm for x = 0 to 1.0065 nm for x = 1. Cu⁺, In³⁺, and Fe²⁺ ions occupy tetrahedral A sites of the spinel lattice and Cr³⁺ ions the octahedral B sites. Spinels with 0 ≤ x ≤ 0.82 are ferrimagnets with Curie temperatures decreasing from 171 K for x = 0 to 116 K for x = 0.82. Spinels with 0.82< x≤ 1 are antiferromagnets with Néel temperatures between 31 K and 36 K. The magnetic moment of Fe_0.18Cu_0.41In_0.41Cr₂S₄ spinels was determined by susceptibility measurements to be 5.85 $\text{μ}{}_{\mathrm{<mtext>B</mtext>}}\text{molecule}$, which is equal to the calculated spin-only magnetic moment.     

CuTa2O6 - crystal growth and characterization

The compound CuTa₂O₆ has been prepared as crystals from a Cu/O melt and found to be tetragonal ($\text{a}\text{= 7.510}\text{A}\text{?}$, $\text{c}\text{= 7.526}\text{A}\text{?}$) rather than cubic as reported in the literature. The coefficient of thermal expansion between room temperature and 1000°C was found to be 8.0 × 10^?6°C^?1. Electrical resistivity measurements on a crystal showed semiconductor behavior between room temperature ($\text{? = 2 × 10}{}^3\text{Ω}\text{cm}$) and 140°K ($\text{? = 7 × 10}{}^6\text{Ω}\text{cm}$) with an activation energy of E_A = 0.2 eV. Magnetic measurements between 4.2°K and room temperature showed Curie-Weiss behavior with a change in μeff at 120°K. For T>120°K, μeff = 1.76μ_B and θ_p = 0°K while for T<120°K μeff = 1.91 μB and θ_p = ?15°K.     

Sodium deintercalation from α-NaFeO2

Chemical deintercalation was investigated on α-NaFeO₂ using bromine as oxidizing agent. The product had a composition about Na_0.9FeO₂ keeping the host layer structure as it was. The crystal lattice was hexagonal and the lattice parameters were $\text{a}\text{=2.997}\text{A}\text{?}$, $\text{c}\text{=16.32}\text{A}\text{?}$. Mössbauer spectrum showed the presence of Fe⁴⁺ in the product. Electrical resistivity was higher than 10⁸Ωcm at room temperature. Na_0.9FeO₂ decomposed to a mixture of α-NaFeO₂ and Fe₃O₄-like ferromagnetic materials above 130°C.     

Temperature induced phase transformation of metastable Fe(OH)3 in the presence of ferrous ions

Reactivity of ferrous and ferric ions has been investigated by means of $\text{re}$ dox potential measurements at room temperature and at 85°C. Results show that in the pH range 6.5–8.0 the prevailing redox system at room temperature is $\text{ra}$ presented by Fe(OH)₃/Fe²⁺; upon heating, the system transforms to Fe₃0₄/Fe²⁺ by a reaction which does not seem to involve the Schikorr reaction. The change of composition of the solid phase is interpreted as a phase transformation of Fe(OH)₃ due to an interaction with Fe²⁺.     

Growth of Ca3Fe2Ge3O12 and Ca3Fe(Al,Cr) Ge3O12 garnets in molten bismuth germanate glasses

Additions of Fe₂O₃ to CaO·Bi₂O₃·2 GeO₂ cause Ca₃Fe₂Ge₃O₁₂ garnets to precipitate from the resultant melt at 1250°C. Garnets with the composition Ca₃Fe(Al, Cr) Ge₃O₁₂ are also precipitated by adding either $\text{Al}{}_2\text{O}{}_3\text{Fe}{}_2\text{O}{}_3$ or $\text{Cr}{}_2\text{O}{}_3\text{Fe}{}_2\text{O}{}_3$ mixtures. The well-formed crystals range from several to 100 μm in size and are obtained in 50 to 70% yields at $\text{Fe}\text{Bi}\text{= 0.4}$. Additions of Fe₂O₃ (up to $\text{Fe}\text{Bi}\text{= 1.0}$) to compositions containing ZnO, CdO, SrO, and BaO yield only dark glasses. The physical properties of these glasses suggest that Fe(III), in contrast to AL(III) & Ga(III), prefers octahedral coordination.     

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.     

The magnetic properties of Fe(OH)2

Ferrous hydroxide free from oxidation was prepared by precipitation from an aqueous solution in an inert gas atmosphere and measured for magnetic susceptibility and magnetization. The antiferromagnetic transition was observed at 34 K, where the susceptibility showed a sharp maximum. The magnetization at 4.2 K increased as the external field increased, and reached 3.6 $\text{μ}{}_{\mathrm{B}}$ per ion at 75 KOe, which is about 90 % of the saturation magnetization of Fe⁺⁺ ion. By analyzing the magnetization curve and the Mössbauer effect, the magnetic structure in an ordered state was deduced as follows: the moments within the layer are arrayed parallel, while those between the adjacent layers antiparallel. The spin easy axis lies in the c-plane. The quadrupole splitting was 3.00 mm/sec at 90 K and showed little temperature dependence between 4.2 K and room temperature. The energy state of Fe⁺⁺ ion in Fe(OH)₂ was specified by the orbital singlet 5A_1g derived from the sign and the magnitude of $\text{1}\text{2}\text{e}{}^2\text{qQ}$. The difference in the magnetic property between Fe(OH)₂ and FeCl₂ was discussed from the energy state of Fe⁺⁺ ion.     

Molybdenum (IV) pyrophosphate isostructural with ZrP2O7

A new molybdenum pyrophosphate, MoP₂O₇, isomorphic with ZrP₂O₇, was prepared at the reductive atmosphere and its magnetic property was measured. The lattice constant of this compound was determined to be $\text{a}\text{=7.952(4)}\text{A}\text{?}$ in the cubic system. A paramgnetic behavior was observed from the liquid N₂ temperature to 500K. The effective magnetic moment for this compound was calculated to be 2.6μ_B in agreement with the calculated spin-only value of 2.83μ_B for Mo⁴⁺.     

High temperature standard gibbs free energy determinations for Co-o systems by e.m.f. measurements. A statistical approach to evaluate the reliability of the current methods

The standard Gibbs free energies of the following reactions: $\text{Co +}\text{1}\text{2}\text{O}{}_2\text{? CoO}$ (1) and $\text{3CoO +}\text{1}\text{2}\text{O}{}_2\text{? Co}{}_3\text{O}{}_4$ (2) have been calculated from the e.m.f. measurements carried out using a simple compartment solid state galvanic cell, as well for the reaction: 3Co + 20₂ ? Co₃O₄ (3) The temperature-equilibrium oxygen partial pressure relationship has been evaluated. A phase diagram for Co, CoO and Co₃O₄ is proposed in the temperature range 600–900 °C. A statistical analysis on reported ΔG_f⁰ values at 1100 K for reaction (1) has been performed and the results are discussed.     

Magneto-torque measurement on V6O13

Magnetic anisotropy of V₆O₁₃ was investigated by the magneto-torque and the magnetic susceptibility measurement in the temperature range from 4 to 300 K. It has been clarified that V₆O₁₃ is antiferromagnetic below about 50 K and the direction of antiferromagnetic spin is parallel to the $\text{b}$-axis.