排序方式: 共有23条查询结果,搜索用时 15 毫秒
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Olfa Labidi Rose-Noëlle Vannier Jean-Pierre Wignacourt 《Journal of solid state chemistry》2008,181(9):2268-2273
Reinvestigation of PbBiOXO4 (X=V, P, As) thermal behaviour revealed a phase transition for V- and P-compounds, but no transition for the As-compound. As shown by single-crystal X-ray diffraction and high-resolution neutron powder diffraction, α-PbBiOVO4 transforms to β-PbBiOVO4 at 550 °C. The two PbBiOPO4 varieties are isomorph to the vanadate forms, while PbBiOAsO4 adopts the β-type structure whatever the temperature. PbBiP1−xOAsxO4 and PbBiV1−xOMxO4 (M=As, P, Cr, Mn) solid solutions display both triclinic and monoclinic domains, and the α→β transition temperature is a function of the substitution rate. The ionic conductivity of these compounds was investigated by impedance spectroscopy. The analysis of free space in the β-PbBiOVO4 structure allows to propose a one-dimensional oxygen diffusion pathway along [010] when the temperature increases. 相似文献
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T. Guedira J. P. Wignacourt M. Drache A. Lorriaux-Rubbens F. Wallart 《Phase Transitions》2013,86(1-4):81-85
Using high-purity starting materials, we synthesized a new room-temperature Cs2KInCl6 phase (I): monoclinic (C2/c), a = 25.484(11), b = 7.699(2) and c = 13.225(3) Å, β = 100.69(3)°. A ferroelasticparaelastic phase transition is noted at Tc = 100°C (by Thermal Analysis and X-ray, Raman-scattering, electrical permittivity versus temperature) leading to the prototype Fm3m phase(II) with a = 10.870(5) Å, quenchable when very slightly spoiled by impurities. 相似文献
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Lotfi Rghioui Lahcen El Ammari Larbi Benarafa Jean Pierre Wignacourt 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(7):i90-i91
The crystal structure of dipotassium caesium ytterbium bis(phosphate) is built up from regular independent PO4 tetrahedra and YbO6 octahedra sharing corners and arranged in layers. The structure is, in many respects, similar to that of glaserite. 相似文献
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Bentiss F Lagrenée M Mentré O Conflant P Vezin H Wignacourt JP Holt EM 《Inorganic chemistry》2004,43(6):1865-1873
Mu-chloro-mu-[2,5-bis(2-pyridyl)-1,3,4-thiadiazole] aqua chlorocopper(II) dichlorocopper(II) is the first characterized dimeric complex of a transition metal and this hetero ligand [C(12)H(10)Cl(4)Cu(2)N(4)OS; triclinic; space group P; a = 9.296(3) A, b = 9.933(3) A, c = 10.412(3) A; alpha = 79.054(5) degrees, beta = 82.478(6) degrees, gamma = 67.099(5) degrees; Z = 2 at room temperature]. The Cu(II) ions are bridged by the N-N thiadiazole bond and a chloride ion [Cu1-Cu2 = 3.7800(8) A]. Thermogravimetric analysis shows this structure to be stable at temperatures up to 348 K. At higher temperatures, the successive loss of a water molecule and one chloride of the dimeric unit is identified. From room temperature to 125 K, half of the Cu(2+) ions are progressively engaged in intermolecular dinuclear antiferromagnetic exchanges, while the other half remain paramagnetic. At lower temperatures, both susceptibility and electron paramagnetic resonance measurements show the paramagnetic-only couplings of this half of the Cu(2+) ions, involving a singlet ground state for interacting Cu(2+). This unusual behavior has been satisfactorily explained on the basis of intermolecular Cu-Cu interactions (J = -180 cm(-1)), involving the magnetic d(z)2 orbital perpendicular to the molecular plane, on which are seen the conjugate effects of the bridging chloride and the planar thiadiazole. It is noteworthy that the behavior of the title compound is original, compared to the systematic in-plane intramolecular antiferromagnetic coupling of other thiadiazole-containing binuclear complexes. 相似文献
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Abstract The Na3PO4-BiPO4 system has been investigated by X-ray diffraction and D.T.A. It features two definite compounds: Na3Bi(PO4)2 and Na3Bi5(PO4)6, the first one being polymorphic. It crystallizes in two orthorhombic and two hexagonal forms below melting at 1025°C. The H.T. phase has the glaserite structure, and the other ones are related. Na3Bi5(PO4)6 is stable only at 680 ? t ? 820°C, but can easily be quenched. It has a non-centrosymmetric cubic structure (S.H.G.) of the eulytite type, and so potential piezoelectric applications can be expected. Na3PO4 and Na3Bi(PO4)2 display two extensive ranges of solid solutions with the replacement mechanism 3Na+ → Bi3+ in the formula Na3-3x Bi x PO4, respectively with 0 ? x ? 0.29 and 0.5 ? x ? 0.62 over 950°C. 相似文献
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