Pseudo Jahn-Teller effect in permittivity of ferroelectric perovskites

[摘要] Microscopic origin of dielectric susceptibility and permittivity of cubic ferroelectric perovskites ABO3(BaTiO3, KNbO3, etc.) in their high-symmetry paraelectric phase is explored. Ferroelectricity in these crystals is due to the strong pseudo Jahn-Teller effect (PJTE) resulting in off-centre instability of the transition metal ion B. In addition to the noticed earlier big enhancement of the permittivity by the local PJTE, it is found that the latter induces also anisotropy, contrary to widespread expectation for isotropic polarization in cubic crystals. The temperature and field dependence of polarization, dielectric susceptibility, and permittivity, as well as their angular dependence, are revealed as resulting from the local PJTE instability by numerical diagonalization of the Hamiltonian including the vibronic coupling and temperature-averaged interaction with the external electric field.

[发布机构] Department of Chemistry, University of Washington, 109 Bagley Hall, Seattle; WA; 98195, United States^1;Institute for Theoretical Chemistry, University of Texas at Austin, 105 E. 24th St., Austin; TX; 78712, United States^2

[关键词] Angular dependence;Diagonalizations;Dielectric susceptibility;External electric field;Ferroelectric perovskites;Field dependence;Paraelectric phase;Vibronic coupling