The harmonon soft modes in a perovskite structure system
钙钛矿结构中的简谐子软模

By using the complex species method, the harmonic vibrational modes of finite crystals having perovskite structure with free boundary condition were obtained. The convergent distribution function of harmonon was given and many harmonon soft modes were found. These soft modes were used to explain the phenomenon that barium titanate crystal has the structure of a domain and c domain in ferroelectric phase transition when temperature is reduced. The theory indicated that the process of ferroelectric phase transition was involved in the excitation of screen charges and their slow diffusion on the interface, till the homogeneous spontaneous polarization appears within each electric domain.