Electronic Structure, Plane Acoustic Velocities and Refractive Properties of LiNbO$lt;inf$gt;3$lt;/inf$gt; and LiTaO$lt;inf$gt;3$lt;/inf$gt;

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 [00 1] directions. The 无 机 材 料 学 报 第 31 卷 calculated static dielectric constants and optical permittivity indicate the refractive index of LiNbO 3 is stronger than that of LiTaO 3 .

Nanoscopic Characterization and Mechanism Analysis of LiTaO3/Si Interfaces Prepared by Mo/Au Nanoadhesive Layers for Applications in LiTaO3-Based Devices

“…The chemical bonds theory indicates that Li, Ta, and O atoms have two types of bonds, and Mulliken population analysis exhibits that there are two corresponding overlapping populations. The Ta–O covalence is stronger than that of Li–O, and the band length is shorter than that of Li–O . After surface activation, Mo atoms replace Li atoms to form Mo–Ta–O chemical bonds with Ta and O atoms.…”