Magnetic interactions in the oxide systems LaNi1−xMxO3 (M = Cr,Fe, or Co)

Magnetic susceptibilities of several members of the series of oxides of the general formula LaNi_1?xM_xO₃ (M = Cr, Fe, or Co) are reported. The oxides show evidence for interesting ferrimagnetic (Cr and Co) and antiferromagnetic (Fe) interactions.     

Relative stabilities of layered perovskite and pyrochlore structures in transition metal oxides containing trivalent bismuth

In order to investigate the factors determining the relative stabilities of layered perovskite and pyrochlore structures of transition metal oxides containing trivalent bismuth, several ternary and quaternary oxides have been investigated. While d⁰ cations stabilize the layered perovskite structure, cations containing partially-filled d orbitals (which suppress ferroelectric distortion of MO₆ octahedra) seem to favor pyrochlore-related structures. Thus, the vanadium analogue of the layered perovskite Bi₄Ti₃O₁₂ cannot be prepared; instead the composition consists of a mixture of pyrochlore-type Bi_1.33V₂O₆, Bi₂O₃, and Bi metal. The distortion of Bi_1.33V₂O₆ to orthorhombic symmetry is probably due to an ordering of anion vacancies in the pyrochlore structure. None of the other pyrochlores investigated, Bi₂NbCrO₇, Bi₂NbFeO₇, TlBiM₂O₇ (M = Nb, Ta), shows evidence for cation ordering in the X-Ray diffraction patterns, as indeed established by structure refinement of TlBiNb₂O₇.     

Durene-rhodium(I) complexes. Crystal structures of the complexes [Rh(durene)(diolefin)]ClO4 (diolefin  tetrafluorobenzobarrelene or trimethyltetrafluorobenzobarrelene)

The crystal structures of [Rh(durene)(diolefin)ClO₄ (diolefin  tetrafluorobenzobarrelene (TFB) and trimethyltetrafluorobenzobarrelene (Me₃TFB)) have been solved by standard X-ray single crystal methods. The compounds crystallize in the space groups R₃c for the unmethylated TFB compound and P2₁/n for the methylated one. The cell dimensions are 25.7586(5), 17.0059(4) Å and 12.6686(6), 11.5565(3), 16.7269(8) Å, β  104.023(5)°, respectively. The refinement was taken to R values of 0.04 and 0.06, respectively. The arene in the TFB derivative has a distorted inverted boat conformation which becomes a skew one in the Me₃TFB compound. These puckering seems to be related to the tendency of rhodium(I) to achieve square-planar coordination.     

Synthesis of robustin and related 4-hydroxy-3-phenyl coumarins and isoflavones

Robustin (31a) occurring in the roots of Derris robusta has been synthesised from mono-O-methylphloroglucinol (20) as follows. Hoesch condensation with homopiperonitrile (21) gave 2,4-dihydroxy-6-methoxyphenyl 3,4-methylenedioxybenzyl ketone (22) which on reaction with 2-hydroxy-2-methyl-3-butene in the presence of borontrifluoride-etherate afforded 5-C-(24) and 3-C-(23) prenyl derivatives. These on cyclodehydrogenation with DDQ followed by coumarin condensation with ethyl chloroformate yielded robustin (31a) and isorobustin (32) respectively. Model experiments with nuclear prenylation of 2,4-dihydroxy-6-methoxy-phenyl benzyl ketone (1), followed by oxidative cyclisation and either courmarin or isoflavone condensation have yielded new isopentenylated 4-hydroxy-3-phenylcourarins or isoflavones.     

Crystal growth and electrical properties of lithium,rubidium, and cesium molybdenum oxide bronzes

Crystals of Li_0.33 MoO₃ (blue), Rb_0.23MoO₃ (blue) and Cs_0.31MoO₃ (red) were grown by electrolysis from MoO₃M₂MoO₄ melts (M =alkali metal) with composition 70–77 mole% MoO₃. Melts richer in M₂MoO₄ produced MoO₂ only. Correlation is made between bronze formation and the coordination of Mo in the melt and in the equilibrium solid phase M₂Mo₄O₁₃. Li_0.33MoO₃ and Cs_0.31MoO₃ are semiconductors with high-temperature-range activation energies 0.16 and 0.12 eV. Rb_0.23MoO₃ has an electrical behavior similar to that of blue K_xMoO₃ with a semiconductor-metal transition at (170 ± 5) K. ESR spectra observed in Li_0.33MoO₃ and Rb_0.23MoO₃ single crystals at 4.2 K show extensive delocalization of the 4d¹ electron associated with Mo(V) centers. Attempts to grow molybdenum bronzes containing Ca or Y were unsuccessful.     

Preparation and characterization of the catalytically active forms of rare earth oxides

Catalytically active forms of the rare earth oxides Ln₂O₃(Ln = La, Sm, Eu, Dy, Ho, and Yb), Pr₆O₁₁, and CeO₂ have been prepared. The dehydration behavior of the precursors of these oxides has been studied by XRD, TG, DTA, TPD-MS, IR, and adsorption-desorption isotherms of N₂ at −196°C. Thermal analyses show that in most cases the dehydration takes place through an intermediate oxyhydroxide LnO (OH) that decomposes to the respective oxide at around 400°C. Strongly held difficult to remove carbonates were present on the surface, e.g., for Yb₂O₃ it was necessary raise the outgassing temperature to 700°C to achieve carbonate decomposition. At temperatures around 500°C these oxides are well crystallized and have moderate specific surface areas (10–40 m²g⁻¹). As a representative of the series, a detailed study of the dehydration and surface decarbonation of Yb₂O₃ was carried out by means of TPD-MS and infrared spectroscopy.     

Electrical and optical properties of high-purity p-type single crystals of GeFe2O4

Single crystals of the spinel GeFe₂O₄, grown by the chemical vapor transport technique, are p-type semiconductors with an acceptor ionization energy of 0.39 eV. The material is a heavily compensated band-type semiconductor, with a typical hole concentration of 10¹⁴ cm^?3 near room temperature, and a temperature-independent Hall mobility of 2 cm²/V·sec. Optical absorption measurements show the optical band gap to be ?2.3 eV; the octahedral field splitting of the Fe²⁺d-levels is 10 200 cm^?1. Magnetic measurements show that n_eff is 5.26, from which a trigonal field splitting of 950 cm^?1 is derived.     

Preparation and photoelectronic properties of the system Cd2Ge1−xSixO4

Members of the system Cd₂Ge_1?xSi_xO₄ where 0 ≤ x ≤ 0.4 have been prepared. These compounds were observed to crystallize with the olivine structure, space group Pbnm. The resistivity, Hall mobility, flat-band potential, band gaps, and stability were determined as functions of composition. The variation of these photoelectronic properties can be attributed to the reduction of the cell parameters with increasing silicon substitution. The substitution of silicon for germanium reduces the loss of photocurrent from 25% after 1 hr for x = 0.0 to only 6% after 22 hr for x = 0.4.     

Ca7Au3 and Ca5Au4, two structures closely related to the Th7Fe3 and Pu5Rh4 types

Two new intermetallic compounds have been synthetized and structurally studied by single crystal diffractometric data: Ca₇Au₃ (oP80, space groupPbca,a = 20.742(8), b = 18.036(8), c = 6.665(2) A?,Z = 8, R = 0.051) and Ca₅Au₄ (mP18, space groupP2₁/c, a = 8.028(3), b = 8.019(6), c = 7.727(3) A?, β = 109.16(6)°,Z = 2, R = 0.104). Both atomic arrangements, which represent new structural types, are based on Au-centered Ca trigonal prisms and are geometrically related to the Th₇Fe₃ and Pu₅Rh₄ structures.     

Dissociation and solubility variation versus pO2- of scheelite CaWO4 in molten NaCl−KCl (At 1000 K)

The conditional solubility of scheelite CaWO₄ in molten NaCl?KCl (1:1) has been studied either in oxobasic or oxoacidic media. In the former case it is increased by formation of sparingly soluble CaO according to:Ca²⁺ + O²CaO(s), pK_s^CaO = 10800/T ? 5.8 (molality scale) In the later case, WO₄^2- behaves as an oxobase according to the following equilibria:WO₄^2?WO₃ (s) + O^2? pK₀ = 10.0 at 1000 K3 WO₄^2?W3O₁₀^2? pK₃ = 12.7 at 1000KThe latter equilibrium favours an increase in the W^VI solubility when pO^2- is increased, for instance by injection of HCl. The whole set of results has been summarized by a conditional solubility diagram of scheelite versus pO^2-.     

Heat capacity and thermodynamic functions of MnBr2 · 4D2O and MnCl2 · 4D2O

The heat capacities of MnBr₂ · 4D₂O and MnCl₂ · 4D₂O have been experimentally determined from 1.4 to 300 K. The smoothed heat capacity and thermodynamic functions (H°_TH°₀) and S°_T are reported for the two compounds over the temperature range 10 to 300 K. The error in the thermodynamic functions at 10 K is estimated to be 3%. Additional error in the tabulated values arising from the heat capacity data above 10 K is thought to be less than 1%. A λ-shaped heat capacity anomaly was observed for MnCl₂ · 4D₂O at 48 K. The entropy associated with the anomaly is 1.2 ± 0.2 J/mole K.     

Preparation and electronic properties of MoS2 and WS2 single crystals grown in the presence of cobalt

Single crystals of MoS₂ and WS₂ were grown by chemical vapor transport in both the presence and absence of cobalt. Hall measurements indicate that cobalt cannot diffuse appreciably into the bulk of MoS₂ or WS₂ and, therefore, can be present only on the surface. Similar results were obtained for as-grown crystals annealed or sulfided in contact with Co₉S₈ or sulfided after being dipped in a 0.1M CoSO₄/methanol solution.     

Defect structures in the brannerite-type vanadates: VI. Preparation and study of Co1−x∅xV2−2xMo2xO6 and phase diagram of the ternary CoO-V2O5-MoO3 system

The phase diagram of the ternary CoO-V₂O₅-MoO₃ system and in particular its T-CoV₂O₆-MoO₃ slice have been determined with DTA and X-ray phase analysis. CoV₂O₆ crystallizes in two modifications: a low-temperature γ-form of unknown structure and a high-temperature α-form of brannerite-type structure. The transition temperature is 660-665°C. The γ ? α transformations are very slow and the α-polymorph may be easily frozen. On doping with MoO₃, a solid solution is formed that is described by the formula Co_1?x?_xV_2?2xMo_2xO₆. Above x = 0.02 the α-type structure is stabilized. The x_max equals 0.22 at the eutectic temperature of 620°C and 0.20 at room temperature. Other features of the phase diagram, including its division into the natural subdiagrams and three ternary eutectics, are described in detail. X-Ray data are listed for α-CoV₂O₆ and for the solid solution having x = 0.20. On doping with MoO₃ the monoclinic lattice dilates primarily in the direction of the b-axis.     

Preparation and properties of the system Fe1−xVxNbO4

Members of the system Fe_1?xV_xNbO₄ were prepared and their crystallographic, electrical, and magnetic properties were determined. The wolframite structure is formed for x ≤ 0.2, but for x ≥ 0.4, a phase transformation to the rutile structure takes place. Magnetic studies established the formal valencies of the elements for members crystallizing with the wolframite phase. However, similar analyses of compounds with the rutile structure did not provide a unique assignment of the formal valencies.     

Spinel, YbFe2O4, and Yb2Fe3O7 types of structures for compounds in the In2O3 and Sc2O3---A2O3---BO systems [A: Fe, Ga, or Al; B: Mg, Mn, Fe, Ni, Cu, or Zn] at temperatures over 1000°C

In the Sc₂O₃---Ga₂O₃---CuO, Sc₂O₃---Ga₂O₃---ZnO, and Sc₂O₃---Al₂O₃---CuO systems, ScGaCuO₄, ScGaZnO₄, and ScAlCuO₄ with the YbFe₂O₄-type structure and Sc₂Ga₂CuO₇ with the Yb₂Fe₃O₇-type structure were obtained. In the In₂O₃---A₂O₃---BO systems (A: Fe, Ga, or Al; B: Mg, Mn, Fe, Ni, or Zn), InGaFeO₄, InGaNiO₄, and InFe³⁺MgO₄ with the spinel structure, InGaZnO₄, InGaMgO₄, and InAlCuO₄ with the YbFe₂O₄-type structure, and In₂Ga₂MnO₇ and In₂Ga₂ZnO₇ with the Yb₂Fe₃O₇-type structure were obtained. InGaMnO₄ and InFe₂O₄ had both the YbFe₂O₄-type and spinel-type structures. The revised classification for the crystal structures of AB₂O₄ compounds is presented, based upon the coordination numbers of constituent A and B cations.     

Preparation and properties of the system Fe1−xCrxNbO4

Members of the system Fe_1?xCr_xNbO₄ were prepared and their magnetic and electronic properties were investigated. It was shown that chromium substitution favored the formation of the rutile structure, which resulted in a decrease in the electrical conductivity because of randomization of the transition metal ions in the structure. The replacement of a few percent of Fe³⁺ with Cr³⁺ caused a significant lowering of the lowest optical band gap, whereas the higher-energy transitions remained essentially unchanged. This resulted in increased response to the longer wavelengths of the solar spectrum.     

Crystal structure of the new thorium intermetallics Thin and Th6Cd7

The title phases are orthorhombic: ThIn,oP24, space groupPbcm,a = 10.806(3)A?,b = 9.954(4)A?,c = 6.520(4)A?,Z = 12; Th₆Cd₇,oP26, space groupPbam,a = 11.703(3),A?,b = 9.929(7)A?,c = 6.041(2)A?,Z = 2. Direct methods were used for both structure solutions on data collected with an automated single crystal X-ray diffractometer. Anisotropic refinements gaveR = 0.065for ThIn andR = 0.086for Th₆Cd₇ using 799 and 1015 reflections, respectively. The structure of ThIn is closely related to the hexagonal Ti₅Ga₄ type, from which it can be geometrically derived. Th₆Cd₇ can be regarded as a tetrahedrally close packed structure where the Th atoms present the typical CN 14, CN 15, and CN 16 Frank-Kasper polyhedra and the Cd atoms are icosahedrally coordinated.     

The crystal and magnetic structures of Sr2YRuO6

Time-of-flight powder neutron diffraction data have been used to refine the crystal structure of the ordered, distorted perovskite Sr₂YRuO₆. Yttrium and ruthenium are octahedrally coordinated in this material with average MO bond lengths of 2.202 and 1.955 Å, respectively. Constant wavelength neutron diffraction data show that Sr₂YRuO₆ is a Type I antiferromagnet at 4.2 K with an ordered magnetic moment of 1.85 μ_B per Ru⁵⁺ ion. The Néel temperature of Sr₂YRuO₆ was determined to be 26 K. The data suggest that the 4d³ electrons in this material are localized rather than itinerant.     

Heat capacity and thermodynamic properties of the alkali metal compounds in the temperature range 300–800 K. I. Cesium and rubidium molybdates

The heat capacities of cesium and rubidium molybdates, Cs₂MoO₄ and Rb₂MoO₄, have been measured by differential scanning calorimetry (DSC) in the temperature range 300–800 K. These values have been combined with published low-temperature heat capacity data for Cs₂MoO₄ to obtain thermodynamic functions to 800 K. For Rb₂MoO₄, however, these functions could not be calculated because low-temperature heat capacities are unavailable. Instead, only heat capacity data are reported.