【摘要】 用西门子D-500型衍射仪,CuKa辐射,收集了不同组分LiNbO_s的X射线粉末衍射图谱。用于研究的样品其Li/Nb比(熔体)是0.88、0.92、0.945、1.00、1.04、1.083。由最小二乘法(2θ=73～105°,16条衍射线)得到各组分的精密点阵参数a,c,其结果表明:a,c随着Li/Nb降低而增加。按四个假设的模型(包括Fay和Lerner的模型)由计算所得到的X射线密度与Lerner的实测密度进行比较,表明对Li/Nb的化学偏离最有希望的解释是部分的铌原子置换锂原子。实验也表明,一致熔化于铌酸锂中的过量铌是按一定方式置换锂。本文系统归纳了由Fay,Lerner和Nassau提出的LiNb_s缺陷结构模型。更多还原

【Abstract】 To bring light to the defect structures of LiNbO₃ crystals, crystalsamples of different compositions were grown from melts with six differentLi/Nb ratios 0.88, 0.92, 0.945, 1.00, 1.04 and 1.083 by the Czochralski technique,and their X-ray powder diffraction patterns were taken with a D-500 diffrac-tometer using CuKα radiation. Accurate values of the lattice parameters aand c of such sample crystals obtained from their X-ray powder diffraction data by the treatment of the least square method show that these latticeparameters increase with the decrease of Li/Nb ratio. On comparising thedensity reported by Lerher with that calculated from the lattice parametersof four hypothetical defect structure models, including those proposed byFay and by Lerner, it seems that the most likely explanation to the non-stoichiometry in the Li/Nb ratio of LiNbO₃ crystals is the partial substitu-tion of lithium atoms by niobium atoms. The excess of Nb atoms in the congruent lithium niobate crystals whichhas been proved by experiments is thought to be the results of substitu-tion in some way. The defect structure models of LiNbO₃ crystals proposedrespectively by Fay, Lerner and Nassau have been summed up systemati-cally in this paper.更多还原