Standard free energy of formation of YFeO3, Y3Fe5O12, and a new compound YFe2O4 in the FeFe2O3Y2O3 system at 1200°C

The phase equilibria in the FeFe₂O₃Y₂O₃ system have been established at 1200°C. The following phases were stable: yttria, hematite, magnetite, wüstite, metallic iron, yttrium-iron perovskite, yttrium-iron garnet, and a new phase YFe₂O₄, belonging to a rhombohedral crystal system. The YFe₂O₄ compound has a solid solution from YFe₂O_3.905 to YFe₂O_4.000. The standard free energies of formation of YFe₂O_3.905, YFeO₃, and Y₃Fe₅O₁₂ have been determined to be ?96 800 ± 200 cal, ?59 800 ± 200 cal, and ?143 700 ± 600 cal, respectively, from metallic iron, Y₂O₃, and oxygen.     

Activities and their relation to cation distribution in NiAl2O4MgAl2O4 spinel solid solutions

The activity of NiAl₂O₄ in NiAl₂O₄MgAl₂O₄ solid solutions has been measured by using a solid oxide galvanic cell of the type, Pt, Ni + NiAl₂O₄ + Al₂O₃(α)/CaOZrO₂/Ni + Ni_xMg_1?xAl₂O₄ + Al₂O₃(α). Pt, in the temperature range 750–1150°C. The activities in the spinel solid solutions show negative deviations from Raoult's law. The cation distribution in the solid solutions has been calculated using site preference energies independent of composition for Ni²⁺, Mg²⁺, and Al³⁺ ions obtained from crystal field theory and measured cation disorder in pure NiAl₂O₄ and MgAl₂O₄, and assumi g ideal mixing of cations on the tetrahedral and octahedral positions. The calculated values correctly predict the decrease in the fraction, α, of Ni²⁺ ions on tetrahedral sites for 1>x>0.25, observed by Porta et al. [J. Solid State Chem.11, 135 (1974)] but do not support their tentative evidence for an increase in α for x < 0.25. The measured excess free energy of mixing can be completely accounted for by using either the calculated or the measured cation distributions. This suggests that the Madelung energy is approximately a linear function of composition in the solid solutions. The composition of NiOMgO solid solutions in equilibrium with NiAl₂O₄MgAl₂O₄ solid solutions has been calculated from the results and information available in literature.     

An EPR study of solid solutions ZnAl2O4ZnCr2O4

We studied the EPR spectra of ZnAl₂O₄-ZnCr₂O₄ solid solutions. The changes observed in the spectrum with increasing chromium concentration are attributed to the gradual development of magnetic interactions between paramagnetic ions in the solid solution. From the concentration dependence of the intensity of the isolated ions spectrum an approximate value of the range of the exchange interactions is deduced. The spectrum observed at high chromium concentrations is attributed to clusters of chromium ions coupled by exchange; the temperature dependence of its intensity indicates an antiferromagnetic character of the concentrated solid solutions.     

The standard free energy of formation of YbFe2O4, Yb2Fe3O7, YbFeO3, and Yb3Fe5O12 at 1200°C

The standard free energy of formation of YbFe₂O₄, Yb₂Fe₃O₇, YbFeO₃, and Yb₃Fe₅O₁₂ from metallic iron, Yb₂O₃, and oxygen was determined to be ?100.38, ?158.38, ?58.17, and ?283.40 kcal/mole, respectively, at 1200°C on the basis of the phase equilibria in the FeFe₂O₃Yb₂O₃ system. The FeFe₂O₃-Lanthanoid sesquioxide systems were classified into four types with respect to the assemblage of the ternary compounds in stable existence at 1200°C, and the standard free energy of formation of YbFeO₃ was compared with those of the other lanthanoid-iron perovskites.     

Polymer-supported calix[4]arenes for sensing and conversion of NO2/N2O4

The use of simple calix[4]arenes 1a,b for NO₂/N₂O₄ sensing and conversion is demonstrated, both in solution and in the solid state. Upon reacting with these gases, compounds 1a,b encapsulate reactive NO⁺ cations within their cavities with the formation of deeply colored (λ_max∼570 nm) charge-transfer complexes 2a,b. Further functionalization of the calix[4]arene platform is reported for attachment to solid supports. Polymer-supported calixarene material 3 was prepared, which reversibly traps NO₂/N₂O₄ with the formation of nitrosonium storing polymer 4. Material 4 was effectively used for nitrosation of amides.     

Thermodynamic properties and cation distribution of the ZnFe2O4Fe3O4 spinel solid solutions at 900°C

The thermodynamic properties of the Fe₃O₄ZnFe₂O₄ spinel solid solution were determined at 900°C by the use of the solid electrolyte galvanic cell Fe₂O₃ + Fe₃O₄|O^2?|Fe₂O₃ + Zn_xFe_3?xO₄The activity values obtained exhibit slight negative deviation from the ideal solution model. An analysis of the free energy of mixing of the spinel solid solution provided information on the distribution of cations between the tetrahedral and octahedral sites of the spinel lattice. This is the basis for the estimation of the free energy of formation of pure zinc ferrite from oxides. ΔG⁰_ZnFe2O4 = ?2740 ? 1.6 T cal 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.     

Thermodynamics of CoAl2O4-CoGa2O4 solid solutions

CoAl₂O₄, CoGa₂O₄, and their solid solution Co(Ga_zAl_1−z)₂O₄ have been studied using high temperature oxide melt solution calorimetry in molten 2PbO·B₂O₃ at 973 K. There is an approximately linear correlation between lattice parameters, enthalpy of formation from oxides, and the Ga content. The experimental enthalpy of mixing is zero within experimental error. The cation distribution parameters are calculated using the O’Neill and Navrotsky thermodynamic model. The enthalpies of mixing calculated from these parameters are small and consistent with the calorimetric data. The entropies of mixing are calculated from site occupancies and compared to those for a random mixture of Ga and Al ions on octahedral site with all Co tetrahedral and for a completely random mixture of all cations on both sites. Despite a zero heat of mixing, the solid solution is not ideal in that activities do not obey Raoult's Law because of the more complex entropy of mixing.     

Preparation and photocatalytic activity of ZnO/TiO2/SnO2 mixture

ZnO/TiO₂/SnO₂ mixture was prepared by mixing its component solid oxides ZnO, TiO₂ and SnO₂ in the molar ratio of 4?1?1, followed by calcining the solid mixture at 200-1300 °C. The products and solid-state reaction process during the calcinations were characterized with powder X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) and Brunauer-Emmett-Teller measurement of specific surface area. Neither solid-state reaction nor change of crystal phase composition took place among the ZnO, TiO₂ and SnO₂ powders on the calcinations up to 600 °C. However, formation of the inverse spinel Zn₂TiO₄ and Zn₂SnO₄ was detected at 700-900 and 1100-1200 °C, respectively. Further increase of the calcination temperature enabled the mixture to form a single-phase solid solution Zn₂Ti_0.5Sn_0.5O₄ with an inverse spinel structure in the space group of . The ZnO/TiO₂/SnO₂ mixture was photocatalytically active for the degradation of methyl orange in water; its photocatalytic mass activity was 16.4 times that of SnO₂, 2.0 times that of TiO₂, and 0.92 times that of ZnO after calcination at 500 °C for 2 h. But, the mass activity of the mixture decreased with increasing the calcination temperature at above 700 °C because of the formation of the photoinactive Zn₂TiO₄, Zn₂SnO₄ and Zn₂Ti_0.5Sn_0.5O₄. The sample became completely inert for the photocatalysis after prolonged calcination at 1300 °C (42 h), since all of the active component oxides were reacted to form the solid solution Zn₂Ti_0.5Sn_0.5O₄ with no photocatalytic activity.     

The crystal structures of the lithium-inserted metal oxides Li0.5TiO2 anatase,LiTi2O4 spinel,and Li2Ti2O4

The crystal structures of three lithium titanates by neutron diffraction powder profile analysis were determined. The tetragonal anatase form of TiO₂ becomes orthorhombic on ambient-temperature lithium insertion to Li_0.5TiO₂ due to the formation of TiTi bonds. The lithium partially occupies the highly distorted octahedral interstices in the anatase framework in fivefold-coordination with oxygen. Cubic LiTi₂O₄ formed by heating Li_0.5TiO₂ anatase has a normal spinel structure with Li in the tetrahedral sites. In Li₂Ti₂O₄ formed by reacting LiTi₂O₄ spinel with n-BuLi at ambient temperature, the titanium remains in the spinel positions but the lithium is displaced, filling all the available octahedral sites.     

Subsolidus phase relations in the systems CeO2RE2O3 (RE2O3 = C-type rare earth sesquioxide)

The systems CeO₂RE₂O₃ (RE₂O₃ = C-type rare earth sesquioxide) were studied to: (1) investigate the claims of several workers for the existence of a complete solid solution series between CeO₂ and RE₂O₃ and (2) to characterize the weak C-type X-ray diffraction peaks reported by others from samples in the single-phase fluorite solid solution region. It is shown that a complete solid solution series does not exist, and an explanation for the observations of others reporting such is tendered. It is also shown that the observation of C-type reflections in the supposed single-phase fluorite field can be attributed to the partial reduction of Ce⁴⁺ to Ce³⁺ at the firing temperature, resulting in the movement of the bulk composition into a two-phase field of the CeO₂RE₂O₃Ce₂O₃ phase diagram, rather than the formation of a domain structure due to ordering.     

Some clues about the interphase reaction between ZnO and MnO2 oxides

Raman spectroscopy is used to evidence both the nature of the interphase reaction between ZnO and MnO₂ particles and its kinetic evolution. Zn cations migrate from the ZnO grains during oxygen vacancies formation process and diffuse into the MnO₂ particles leading to an interphase region with an intermediate valence Mn⁺³-O-Mn⁺⁴. Large amounts of desorbed Zn cations promote the formation of ZnMn₂O₄ structure, in addition to the intermediate valence state. The system evolves towards complete formation of the spinel phase at higher thermal treatment times. The reactivity of the ZnO plays an important role in the formation of this interphase. Low-reactivity ZnO powder, in which the oxygen vacancies are previously produced, shows a stabilization of the intermediate valence state with very limited formation of the spinel phase. A clear correlation between the amount of the intermediate state interphase and the magnetic properties has been established.     

The system NiAl2O4Ni2SiO4 at high pressures and temperatures: Spinelloids with spinel-related structures

Phase relations in the system NiAl₂O₄Ni₂SiO₄ were studied in the pressure range 1.5 ～ 13.0 GPa and in the temperature range 800 ～ 1450°C. Two new phases, IV and V, were found in regions of pressure higher than 4 GPa. Phase V disproportionates into a mixture of Ni₂SiO₄-spinel, NiO, and Al₂O₃ at approximately 9.5 GPa and 1100°C. Phases III, IV, and V form a solid solution in some compositional range: phases IV and V have a composition around NiAl₂O₄·Ni₂SiO₄, whereas phase III spreads from NiAl₂O₄·Ni₂SiO₄ to the NiAl₂O₄-rich side. All the phases I ～ V are structurally considered to be spinel derivatives, “spinelloids,” with three kinds of tetrahedral groups; isolated tetrahedra TO₄, linked ones T₂O₇, and triply linked ones T₃O₁₀. The ratios of isolated tetrahedra to linked ones are large in the higher-pressure phases and small in the lower-pressure phases. The difference of compositional range of phase III from that of phases IV and V is possibly explained by the avoidance of linked tetrahedra such as O₃AlOAlO₃.     

Magnetic diphase nanostructure of ZnFe2O4/γ-Fe2O3

Magnetic diphase nanostructures of ZnFe₂O₄/γ-Fe₂O₃ were synthesized by a solvothermal method. The formation reactions were optimized by tuning the initial molar ratios of Fe/Zn. All samples were characterized by X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, and Raman spectra. It is found that when the initial molar ratio of Fe/Zn is larger than 2, a diphase magnetic nanostructure of ZnFe₂O₄/γ-Fe₂O₃ was formed, in which the presence of ZnFe₂O₄ enhanced the thermal stability of γ-Fe₂O₃. Further increasing the initial molar ratio of Fe/Zn larger than 6 destabilized the diphase nanostructure and yielded traces of secondary phase α-Fe₂O₃. The grain surfaces of diphase nanostructure exhibited a spin-glass-like structure. At room temperature, all diphase nanostructures are superparamagnetic with saturation magnetization being increased with γ-Fe₂O₃ content.     

Structure and magnetism of NaRu2O4 and Na2.7Ru4O9

The structures of NaRu₂O₄ and Na_2.7Ru₄O₉ are refined using neutron diffraction. NaRu₂O₄ is a stoichiometric compound consisting of double chains of edge sharing RuO₆ octahedra. Na_2.7Ru₄O₉ is a non-stoichiometric compound with partial occupancy of the Na sublattice. The structure is a mixture of single, double and triple chains of edge-shared RuO₆ octahedra. NaRu₂O₄ displays temperature independent paramagnetism with . Na_2.7Ru₄O₉ is paramagnetic, χ₀= with and a Curie constant of 0.0119 emu/mol Oe K. Specific heat measurements reveal a small upturn at low temperatures, similar to the upturn observed in La₄Ru₆O₁₉. The electronic contribution to the specific heat (γ) for Na_2.7Ru₄O₉ was determined to be15 mJ/mole_Ru K².     

Theoretical study of the structure and stability of the heme dimer (FeC34H32N4O4)2 and its ion (FeC34H32N4O4) 2+

The electronic and geometric structures and the dissociation energies of the isolated molecule of heme dimer (heme)₂ = (FeC₃₄H₃₂O₄N₄)₂ and its ion (heme) ₂ ⁺ = (FeC₃₄H₃₂O₄N₄) ₂ ⁺ in the states with different multiplicities have been calculated by the density functional theory B3LYP method with the Gen-1 = 6-31G*(Fe) + 6-31G(C,H,N,O) and Gen-2 = 6-311++G*(Fe) + 6-31G*(C,H,N,O) basis sets. The computation results are compared with the analogous calculated data on monomeric heme and hemin⁺, as well as the previously considered dimeric ferriporphyrin X molecule and ion FeC₃₄H₃₁O₄N₄) ₂ ^{0, +} . In the heme dimer cation (heme) ₂ ⁺ , which is identified in mass spectra, the rings are linked with each other by a pair of Fe carbonyl bridges Fe⋯O_b = C(OH) and a pair of hydrogen bridges OH_b⋯N. According to the calculations, the most favorable state for (heme) ₂ ⁺ is the sextet in which five unpaired electrons are approximately uniformly distributed over the metal atoms, whereas the states with higher multiplicities 8 and 10 are, respectively, 0.15 and 0.20 eV higher on the energy scale. For the neutral dimer (heme)₂, the quintet is favorable in which each of the two Fe atoms has two unpaired electrons, and the states with the higher multiplicities 7 and 9 are only 0.10–0.15 eV higher. The calculated energies of dissociation D of the dimers into monomers point to a rather high stability of the (heme) ₂ ⁺ (D ∼ 1.4 1.4eV) and to a low stability of the neutral dimer (heme)₂ (D ∼ 0.3 eV). The R(Fe⋯O_b) distances in the bridges in (heme) ₂ ⁺ are 0.2–0.4 ? shorter than in (heme)₂. The trends in the behavior of the energetic and structural characteristics of the dimers (R(Fe-N), displacements of Fe atoms from the porphyrin ring plane, character of ring distortions, etc.) associated with the involvement of the and AOs of Fe atoms in bonding, as well as the spin density distribution over the Fe atoms and the rings, are analyzed as a function of the multiplicity and charge of the system. Differences in the character of interaction of the heme and ferriporphyrin dimers with molecular oxygen are discussed. Original Russian Text ? O.P. Charkin, N.M. Klimenko, D.O. Charkin, S.H. Lin, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 7, pp. 1166–1174.     

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.     

Thermochemistry of NaRb[B4O5(OH)4]·4H2O

The enthalpies of solution of NaRb[B₄O₅(OH)₄]·4H₂O in approximately 1 mol dm⁻³ aqueous hydrochloric acid and of RbCl in aqueous (hydrochloric acid + boric acid + sodium chloride) were determined. From these results and the enthalpy of solution of H₃BO₃ in approximately 1 mol dm⁻³ HCl(aq) and of sodium chloride in aqueous (hydrochloric acid + boric acid), the standard molar enthalpy of formation of −(5128.02 ± 1.94) kJ mol⁻¹ for NaRb[B₄O₅(OH)₄]·4H₂O was obtained from the standard molar enthalpies of formation of NaCl(s), RbCl(s), H₃BO₃(s) and H₂O(l). The standard molar entropy of formation of NaRb[B₄O₅(OH)₄]·4H₂O was calculated from the Gibbs free energy of formation of NaRb[B₄O₅(OH)₄]·4H₂O computed from a group contribution method.     

Structure and properties of the CaFe2O4-type cobalt oxide CaCo2O4

The calcium cobalt oxide CaCo₂O₄ was synthesized for the first time and characterized from a powder X-ray diffraction study, measuring magnetic susceptibility, specific heat, electrical resistivity, and thermoelectric power. CaCo₂O₄ crystallizes in the CaFe₂O₄ (calcium ferrite)-type structure, consisting of an edge- and corner-shared CoO₆ octahedral network. The structure of CaCo₂O₄ belongs to an orthorhombic system (space group: Pnma) with lattice parameters, a=8.789(2) Å, b=2.9006(7) Å and c=10.282(3) Å. Curie-Weiss-like behavior in magnetic susceptibility with the nearly trivalent cobalt low-spin state (Co³⁺, 3d, S=0), semiconductor-like temperature dependence of resistivity (ρ=3×10⁻¹ Ω cm at 380 K) with dominant hopping conduction at low temperature, metallic-temperature-dependent large thermoelectric power (Seebeck coefficient: S=+147 μV/K at 380 K), and Schottky-type specific heat with a small Sommerfeld constant (γ=4.48(7) mJ/Co mol K²), were observed. These results suggest that the compound possesses a metallic electronic state with a small density of states at the Fermi level. The doped holes are localized at low temperatures due to disorder in the crystal. The carriers probably originate from slight off-stoichiometry of the phase. It was also found that S tends to increase even more beyond 380 K. The large S is possibly attributed to residual spin entropy and orbital degeneracy coupled with charges by strong electron correlation in the cobalt oxides.     

Isothermal gravimetry and magnetic properties of CoOMoO3γAl2O3 catalysts

Isothermal gravimetry and magnetic susceptibility of MoO₃, MoAl₂O₃, CoAl₂O₃ and CoMoAl₂O₃ with/without Na⁺ ions have been studied in order to investigate the reducibility of the systems in H₂ H₂—hydrocarbons and H₂—hydro-carbon—thiophene. These studies have evidenced the formation of metallic cobalt during reduction of cobalt—moly catalysts containing Na⁺ ions in the Al₂O₃ support. This metallic cobalt accelerates the reduction of supported MoO₃. However, in the absence of sodium, cobalt exerts an inhibitory influence on the reduction of MoAl₂O₃. The inhibition is caused mainly due to retention of the water evolved during the process by well-dispersed Co²⁺ ions which are incapable of undergoing reduction. The presence of sulfur also kelps in suppressing the reduction to cobalt metal.