钽铌酸钾锂晶体结构与光学性能的第一性原理研究

Structure and Optical Properties of Potassium Lithium Tantalite Niobate Crystal: a First-principle Study

为了探索Li掺杂对钽铌酸钾(KTa_(1-x)Nb_xO_3,简称KTN)结构和性能的影响,构建了KTN(KTa_(0.5)Nb_(0.5)O_3)与KL_(0.125)TN(K_(0.875)Li_(0.125)Ta_(0.5)Nb_(0.5)O_3)晶体超晶胞模型,采用第一性原理的密度泛函理论,对模型进行了几何结构优化、电子结构、光学性能和弹性性能的计算与分析.计算结果表明:Li掺杂后晶格常数自3.991减小为3.986,且禁带宽度有所增大.晶体在可见光范围内有较高的折射率,数值随波长的增加而减小,属于正常色散,其柯西方程参数A、B、C分别为1.796 9、-0.010 5、0.008 7;晶体在可见光范围内,特别是大于450 nm时的消光系数较小,说明其良好的透明性.另外,KL_(0.125)TN晶体与KTN晶体相比,其独立弹性常数、体积模量、剪切模量、杨氏模量减小,泊松比增大,说明其材料的柔度增加,脆性减小,更有利于实用化.

In order to explore the influence of structure and properties of Li-doped potassium tantalite niobate（ KTa_（1-x）Nb_xO_3,KTN）,the model of KTN（ KTa_（0.5）Nb_（0.5）O_3） and KL0.125TN（ K_（0.875）Li_（0.125）Ta_（0.5）Nb_（0.5）O_3） were established in this paper.The geometry optimization,electronic structure,optical properties and elastic properties of the model were calculated using first-principle density functional theory.The results show that the lattice constants were decreased from 3.991 to 3.986 and the band gap was increased after Li-doped.In the range of visible light,the refractive index decreased with increasing wavelength,which belongs to the normal dispersion and the Cauchy parameters A,B and C are 1.796 9、- 0.010 5、0.008 7,respectively.The extinction coefficient is very low in the range of visible light,especially when the wavelength is bigger than 450 nm,which indicates that the transparency was excellent.In addition,the independent elastic constants,bulk modulus,shear modulus and Young modulus of KL_（0.125） TN crystal,decrease comparing with the KTN crystal,whereas the Poisson ratio increases.The increasing flexibility and decreasing brittleness are propitious to the practical application.