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First‐principles study of structural, electronic, elastic, and optical properties of cubic KNbO 3 and KTaO 3 crystals
Author(s) -
Xu YongQiang,
Wu ShaoYi,
Zhang LiJuan,
Wu LiNa,
Ding ChangChun
Publication year - 2017
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.201600620
Subject(s) - materials science , anisotropy , condensed matter physics , crystallite , molecular physics , optics , chemistry , physics , metallurgy
Cubic KNbO 3 and KTaO 3 crystals are studied using the first‐principles VASP code. By employing local density approximation (LDA), GGA‐PBE, and HSE06, the lattice parameters are optimized and compared with available experimental data, and the best agreement is achieved with HSE06. Electronic structures such as density of states, band structures, and charge‐density distribution are discussed in detail for both crystals. The single‐crystal elastic constants, polycrystalline elastic modulus, compressibility, Poisson's ratio, and anisotropy factors are obtained from the Voigt–Reuss–Hill approximation. The elastic anisotropy is modeled and visualized in the light of the elastic properties of both systems. The bandgaps of the two crystals are calculated with LDA, PBE, HSE06, and GW approximations (GW0), and the results of HSE06 and GW0 agree well with experimental data. Then the more reliable optical properties of KNbO 3 and KTaO 3 are acquired based on the bandgaps with HSE06, in which the previous scissors operator correction is avoided. Both crystals are brittle, and KTaO 3 exhibits higher hardness and stiffness than KNbO 3 . Some novel results, such as Debye temperatures, sound velocities, and the extreme values of Young's modulus are obtained.