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1.
A new hydrate of tungsten trioxide, has been obtained by hydrothermal treatment at 120°C of an aqueous suspension of either tungstic acid gel or crystallized dihydrate. This hydrate has been characterized by different methods. A crystallographic study was carried out from X-ray powder diffraction. The hydrate crystallizes in the orthorhombic system: a = 7.359(3) Å, b = 12.513(6) Å, c = 7.704(5) Å, Z = 12. The existence of structural relationships between the hydrate, , and the product of dehydration, hexagonal WO3, has permitted us to propose a structural model in agreement with the experimental data. must be regarded as an interesting compound because its dehydration leads to a new anhydrous tungsten trioxide, hexagonal WO3. 相似文献
2.
The structure of a crystal was established by X-ray analysis. The solution in the cell of symmetry , with a = 6.6702(5), b = 5.3228(8), c = 8.9091(8) Å, β = 100.546(7)°, Z = 1, has led to R = 0.033 and Rw = 0.036 for 2155 reflections with . This structure can be described as two octahedra-wide ReO3-type slabs connected through “planes” of PO4 tetrahedra. A new structural family KxP2W2nO6n+4 can be foreseen which is closely related to the orthorhombic P4W8O32 and the monoclinic RbxP8W8nO24n+16 series. 相似文献
3.
The incongruent vaporization reactions of Ta2S and Ta6S have been investigated by mass-loss effusion in the temperature range 1576 to 1902 K. By extrapolation of PS(obs) to equilibrium the enthalpies of the reactions and Ta6S = 6 Ta(s) + S(g) were found to be and , respectively. Comparison between the above values, determined by a 2nd law treatment, and 3rd law values was used to derive fef (“free energy function”) values for Ta and S in the compounds. These postulated fef's, which apply only to the elements as present in the compounds measured, are compared to tabulated quantities for the pure solid elements to provide a criterion for 2nd and 3rd law evaluation. 相似文献
4.
The amine substituted phosphines (C6H5)2PN(H)CH2CH3 and (C6H5)2PN(H)CH2C6H5 react with C5H5Fe(CO)2CH(C6H5) (OCH3) photolytically to give moderate yields of the four-membered chelate ring complexes C5H5H (C6H5)] and C5H5H(C6H5)], respectively. Photolysis of C5H5Fe(CO)2CH(C6H5) (OCH3) in the presence of (S)-(?)-diphenyl(1-phenylethylamino)phosphine leads to the isolation of C5H5Fe(CO)[(C6H5)2PNC(CH3) (C6H5)]CH2C6H5 which is proposed to arise from a formally 1,3-hydrogen shift rearrangement of an intermediate four-membered chelate ring complex. 相似文献
5.
The distribution of La3+ and Ca2+ over the cation sites in Ca2La8(SiO4)6O2 was determined by single-crystal X-ray diffraction. Ca2La8(SiO4)6O2 has the apatite structure, and all available evidence indicates that the space group is , thus precluding a completely ordered structure. The 6h lattice sites are occupied by La3+. In contrast, the 4f sites are occupied equally by La3+ and Ca2+ ions. Consideration of the properties of the La3+ and Ca2+ ions suggests that this distribution is thermodynamically favored for this composition. A simple Ising model suggests ordered columns. These would not be precluded by space group , if the correlation between adjacent columns were random. 相似文献
6.
The compounds and Ba3.6Al0.4Fe2S6[S0.6(S2)0.4], designated I and II, were prepared by reacting BaS, Fe, and S powders and Al foils in graphite containers sealed in evacuated quartz ampoules at approximately 1100°C. The crystal structure of I was determined using 1682 independent, nonzero X-ray reflections, while 3589 were used for II. They are triclinic, : BaS6 trigonal prisms share edges to form distorted hexagonal rings which form one-dimensional chains leaving two free lateral edges. The chains link in a stairstep manner with the rings offset along the [301] direction. These stairsteps join in a complicated manner to form a three-dimensional network. Fe ions are in two sites forming isolated FeS4 tetrahedra and isolated Fe2S6 dimers by edge-sharing tetrahedra. The Al substitution occurs in the trigonal prisms which have free edges with Al replacing Ba. Room-temperature Mössbauer isomer shifts are 0.20 mm/sec. for I and 0.30 mm/sec for II. These data indicate that upon Al substitution charge compensation occurs by reducing Fe3+. Valence calculations indicate that Fe in edge-sharing tetrahedra are reduced while the Fe in the isolated tetrahedron remains unchanged. The effective charge distribution in the Al substituted compound is approximately Fe3+, Fe2.5+ with electron delocalization across the shared edge. Room temperature electrical resistivity is 105 ohm/cm. The compositions of the crystals are best represented by the formulas and [Ba3AlFe2S7]0.4·[Ba4Fe2S7]0.2·[Ba4Fe2S6(S2)]0.4. The replacement of a sulfide by a disulfide ion is thought to be strongly dependent on the sulfur activity during the preparation. 相似文献
7.
The excess molar enthalpies HmE{(1 ? x2 ? x3)Al + x2Bi + x3Ga}(I) have been measured between 725 and 1170 K along the sections , 1, and 3, and , 1, and 3, with a high-temperature Calvet calorimeter using both the direct- and indirect-drop methods of mixing; experimental uncertainty is quoted respectively at 6.7 per cent and 9.9 per cent. The equilibrium temperatures confirmed phase boundaries previously determined by potentiometry, d.t.a., and calculation. Extrapolation of the experimental excess molar enthalpies to the limiting binary alloys {(1 ? x2)Al + x2Bi} allows new values for the excess molar enthalpies of these alloys to be proposed. The excess molar enthalpies of the ternary liquid mixtures can be represented correctly using these new values and Bonnier's equation. 相似文献
8.
Carl W.F.T. Pistorius 《Journal of solid state chemistry》1975,13(4):325-329
The phase diagram of Li2WO4, previously studied by Yamaoka et al. (J. Solid State Chem.6, 280 (1973)) has been revised. Li2WO4 II is stable at atmospheric pressure below ~310°C. This phase appears to be a modified spinel, and is tetragonal, a, c = 11.941, 8.409Å, Z = 16, space group . The melting curve of phenacite-type Li2WO4 I rises with pressure with a slope of 0.9°C/kbar to the III/I/liquid triple point at 3.1 kbar, 743°C, beyond which the melting curve of orthorhombic Li2WO4 III rises steeply with pressure (initial slope 31°C/kbar). The Li2WO4 transition line at 3 kbar is almost independent of temperature, i.e., the transition entropy is zero. Li2WO4 II is 21.3% denser than Li2WO4 I at ambient conditions. 相似文献
9.
TlGaSe2 and β-TlInS2 were studied for crystal growth and optical properties. Both materials have wide transparency regions, from 0.61 to 20 μm for the former and 0.5 to 12.5 μm for the latter. X-ray studies of single crystals show that these compounds are monoclinic, space group . Raman spectra are presented. 相似文献
10.
The compound Th0.25 NbO3 melts congruently at 1390°C. Single crystals obtained by slow cooling from the melt are transparent and show uniaxial optical properties. A single-crystal X-ray analysis confirms the tetragonal cell found by Kovba and Trunov from a powder data and gives a = 3.90 Å and c = 7.85 Å. No systematic absence of the hkl reflections is observed on precession films. The relative intensities of the main reflections are characteristic of a perovskite-like arrangement ABO3 whose large dodecahedral A sites are only partly occupied. Several domains have been found in the perovskite-type solid solution (1 ? x) Th0.25NbO3-x NaNbO3. For 0 ? x ? 0.5 the phases have a tetragonal cell with and as in pure Th0.25 NbO3. When 0.6 ? x ? 0.8 the corresponding phases crystallize with a small cubic cell (Å), while phases with 0.9 ? x ? 1 have an orthorhombic cell (). 相似文献
11.
This paper gives an outline of the structure of a solid solution based on 7Bi2O3 · 2WO3. The experimental results using X-ray diffraction methods (precession and powder) showed that 7Bi2O3 · 2WO3 crystallizes in the space group with a = 12.5143(5)Å and c = 11.2248(6) Å. The number of formula weights per unit cell is 40, when the formula is considered to be of the oxygen-deficient fluorite-type Bi0.875W0.125O1.6875. The compound has a substructure based on a defect fluorite-type pseudocubic subcell with Å. The axial relations between the supercell and subcell are and . The solid solution was formed over a limited range of WO3 content between 21.3 mole% and 26.3 mole% at 700°C. The ordering of metal atoms is discussed and an ideal crystal structure is proposed. 相似文献
12.
Joaquín García Juan Bartolomé Domingo González Rafael Navarro Willem Jacobus Crama 《The Journal of chemical thermodynamics》1983,15(12):1109-1126
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 Tc = (171.1±0.1) K was detected for CsCrCl3. The RbCrCl3 showed at Tc = (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 TN ≈ 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
CsCrCl3 | 15.38 | 26.49 | 3503.2 | 14.735 |
RbCrCl3 | 15.76 | 25.99 | 3556.8 | 14.384 |