| This dissertation is devoted to an atomistic understanding of the dielectric properties of oxide perovskites, in particular barium titanate (BTO) and strontium titanate (STO).;The BTO, a ferroelectric, undergoes a series of polar structural phase transitions as temperature goes down. Here we focus on the tetragonal-cubic transition that occurs about 410K. Much theoretical work have been invested to clarify the transition mechanism, which pertains basically to the behaviors of the static dielectric constant and hence to the lowest frequency phonon mode. In this dissertation, an atomistic model has been established to achieve proper understanding. With this model, many phenomena become comprehensible in a unified context. It is also applied to STO, which is an incipient ferroelectric. In addition, the implications for cuprate superconductors have been discussed. |
