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M. Marezio D.B. McWhan P.D. Dernier J.P. Remeika 《Journal of solid state chemistry》1973,6(3):419-429
V4O7 has a transition with decreasing temperature at 250 K and the structure has been refined at 298 and 200 K. The triclinic structure (A) consists of rutile-like layers of VO6 octahedra extending indefinitely in the a-b plane and four octahedra thick along the c-axis. The average VO distances for the four independent V atoms are 1.967, 1.980, 1.969, and 1.984 Å at 298K and 1.948, 1.992. 1.961, and 2.009 Å at 200K. At 200K there is a clear separation into strings of V3+ or V4+ ions running parallel to the pseudorutile c-axis. In addition, all of the 3+ and half of the 4+ sites are paired to form short VV bonds. The remaining V4+ atom is displaced toward one oxygen so as to balance its electrostatic charge. The distortion at the metal-insulator transitions in V4O7, Ti4O7, VO2 + Cr, and NbO2 are compared. 相似文献
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The x-ray diffraction intensities of Bragg reflections have been measured at room temperature for thulium selenide, samarium sulphide, samarium selenide and samarium telluride. On the basis of a common amplitude approximation, the Debye-Waller factor, the mean amplitude of vibration and the Debye temperature have been evaluated. The values of the Debye temperatures and mean amplitudes of vibration are 176±16°K, 0·185 ± 0·017 Å (TmSe), 155 ± 7°K, 0·244 ± 0·012 Å (SmS), 153 ± 14°K, 0·221 ± 0·020 Å (SmSe) and 151 ± 20°K, 0·204 ± 0·027 Å (SmTe). 相似文献
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A rigorous investigation of the identification of a heterogeneousflexural rigidity coefficient in the Euler-Bernoulli steady-statebeam theory in the presence of a prescribed load is presented.Mathematically, this study is an extension to higher-order differentialequations of the coefficient identification problem analysedby Marcellini (1982) for the one-dimensional Poisson equation.In addition, various types of boundary conditions are discussed.Conditions for the well-posedness of these inverse problemsare established and, furthermore, numerical results obtainedusing a regularization algorithm are presented. 相似文献