Perovskite-type Ferroelectrics Dv-x_¦Á Of Research

Ferroelectrics materials of perovskite type are the subjects of extensive investigation both because of the fundamental interest in theory research and application importance. Materials design means designing form and property base on performance needed, which is the ultimate aim of the theory research on ferroelectrics materials. With the development of quantum mechanics and solid state physics, materials design by agency of computation aid has been the trend to materials science. The recent decade years, there are many theoretical tools and models being used to study ferroelectrics. The Diacrete Variational Xα method has been played in the large atom clusters and is becoming a powerful and fruitful tool in this field.In general, the main work is as follows:1. The investigation actuality of ferroelectrics materials of perovskite type has been summarized.2. Recite the program used in this paper.3. Investigation on incipient ferroelectric CaTiO3. DV-Xα method was used for the study of incipient ferroelectric CaTiO3. The results showed that: By changing the lattice bulk, the total energy was the minimum with the displacement of titanium ion. Cubic CaTiO3 has the trend to ferroelectric phases transition, which means CaTiO3 is incipient ferroelectric. With a 10% bulk expansion, there is a orbital overlap between Ti 3d and O 2p, which is responsible for the tendency to ferroelectricity.4. Study of pure phases and A site doped PbTiO3. In order to understand pure phases and A-doped PbTiO3, the electronic structure was calculated by the DV-Xα method. It showed that there is a strong orbital reciprocity between Ti 3d and O 2p, which causes the tendency to ferroelectricity. The performance of PbTiO3 material modified by Sr and La atoms was improved.5. Study of pure phases and A site doped BaTiO3.As well known, BaTiO3 is important one of perovskite ferroelectricities. In order to understand the relationship between configuration and property, optimize the initial configuration using Gaussian 03 program. DV-Xα method was used for the study of the electronic structure that the configuration was optimized and not. In the next step, In order to understand pure phases and modified BaTiO3, the electronic structure was calculated by the DV-Xα method. It showed that there is a strong orbital reciprocity between Ti 3d and O 2p, which is responsible for the tendency to ferroelectricity. The performance of BaTiO3 materialmodified by Ca, La and Pb atoms was reformed.6. Invest on ferroelectric solid solution PbZr0.5Ti0.5O3 and A-site doped PbZr0.5Ti0.5O3. PbZr0.5Ti0.5O3 was a complex compound ferroelectric with Zr and Ti occupy the B-site in the ABO3 perovskite structure, in order understand the origin of the ferroelectricity of PbZr0.5Ti0.5O3 and how the displacement affects the performance, DV-Xa method was used to calculated the electric struture of the pure phases and A-doped PbZr0.5Ti0.5O3.In general, Gaussian program and DV-Xα method was used to research the perovskite ferroelectrics. The occupied orbitals, energy level, DOS and total energy was calculated, which was to provide theory reference and performance prediction for design and preparation of ferroelectric materials.