光折变晶体KTa_(0.5)Nb_(0.5)O_3光学特性的第一性原理研究

First principle study on optical properties of KTa_(0.5)Nb_(0.5)O_3

用全电势线性缀加平面波法 (FLAPW)计算了KTa0 5Nb0 5O3四方相和立方相的光学特性 ,即介电函数虚部ε2 (ω)、光学吸收系数I(ω)和反射率R(ω) .在四方相 ,介电虚部沿a ,b轴 ,在 3,7和 2 3eV附近 ,分别有三个介电峰 .沿c轴的三个介电峰分别位于 4 ,8和 2 3eV .其中 4eV附近的介电峰非常尖锐而且高 .从 8至 1 8eV ,沿a ,b ,c轴三个方向都有许多低的介电峰 .通过对两相光学特性的对比分析发现铁电相KTa0 5Nb0

We have calculated the optical properties(the imaginary part of the dielectric function ε 2(ω) ,the optical absorption coefficient I(ω) ,the reflectivity R(ω) ) of tetragonal and cubic crystals of KTa 0 5 Nb 0 5 O 3 by the full potential linearized augmented plane wave method (FLAPW).Our calculated tetragonal optical spectra show three big peaks around 3,7 and 23 eV along a and b separately.Along c ,there are three mainly peaks at 4,8,23 eV respectively,among which the one at 4 eV is sharp and high.Comparing optical properties in the tetragonal and cubic phass,we concluded that the tetragonal phase has more anisotropic optical responses.