Journal of Inorganic Materials ›› 2016, Vol. 31 ›› Issue (2): 171-179.DOI: 10.15541/jim20150338

• Orginal Article • Previous Articles     Next Articles

Electronic Structure, Plane Acoustic Velocity and Refractive Property of LiNbO3 and LiTaO3

SHAO Dong-Yuan, CHENG Nan-Pu, CHEN Jing-Jing, LI Xiao, CHEN Zhi-Qian, LI Chun-Mei, HUI Qun   

  1. (Faculty of Materials and Energy, Southwest University, Chongqing 400715, China)
  • Received:2015-07-14 Revised:2015-10-19 Published:2016-02-20 Online:2016-01-15
  • About author:SHAO Dong-Yuan. E-mail: sdy1988719@swu.edu.cn
  • Supported by:
    National Natural Science Foundation of China (51171156);Fundamental Research Funds for the Central Universities of Ministry of Education of China (XDJK2014C008)

Abstract:

Lattice parameters, electronic structures and elastic constants of lithium niobate and lithium tantalate were calculated with the plane wave pseudopotential method based on the first-principles density functional theory. The results show that calculated lattice parameters and elastic constants are in consistent with the corresponding experimental values. It was found that the bottom of the valence band and the top of the conductive band are mainly determined by electron orbits of O-2p and Nb-4d (Ta-5d). The chemical bonds theory indicate that Li, Nb (Ta) and O atoms have two types of bonds, and the Mulliken population analysis exhibits that there are two corresponding bond populations. The Nb-O (Ta-O) covalence is stronger than that of Li-O, and band length shorter than that of Li-O. Moreover, the planar acoustic velocities, studied by Christoffel equation, shows that the three-dimensional images of the planar acoustic wave consisting of a longitudinal wave and two transverse waves, indicating the anisotropic feature. The velocity of the longitudinal wave is larger than those of the two transverse waves. In xz and yz planes, not only the plane projections of the planar acoustic waves show the stronger anisotropy than those in xy plane which have a six-fold symmetry, but also the velocities of the two transverse waves are equal in [001] and directions. The calculated static dielectric constants and optical permittivity indicate the refractive index of LiNbO3 is stronger than that of LiTaO3.

Key words: first-principles, electronic structure, elastic constants, planar acoustic velocity

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