科研之友
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摘要
The anisotropic nature of the permittivity of tetragonal BaTiO3 has been investigated by means of first-principles calculations using density-functional perturbation theory and constrained-force approaches. Our calculations suggest that the origin of the anisotropy is the presence of a soft mode with very shallow double-well potential surface that results in non-frozen dipole moments parallel to the a-axes of the tetragonal crystal. Even at relatively low temperatures, the dipoles fluctuate back and forth, resulting in net zero dipole perpendicular to the c-axis in the absence of an electric field. The enormous permittivity observed experimentally parallel to the a-axis of tetragonal BaTiO3 is a consequence of the relatively large polarization induced by these small lattice distortions, together with the low energy barrier that needs to be overcome to switch to the polarized structure.
- 出版日期2011-9
