First Principles Theoretical Studies of Ferroelectric Lattice Instabilities

Preliminary work on the theoretical understanding of polar ferroelectric lattice instabilities in ceramic oxides is described. Emphasis is placed on the need to handle electronic charge density redistribution and its effects on lattice instabilities. The emphasis is on doing so with a few variables as possible in order to make molecular dynamics studies of phase stability and other properties possible. In addition, a summary is presented of work carried out to round out studies under our previous ONR Award. The objective of this new program can be stated very simply it is to incorporate the effects of electronic charge redistribution into a calculations of changes in lattice potential energies for arbitrary crystal distortion and thus to predict its influence on the uniform polar antiphase motion of positive and negative ions distortions associated with ferroelectricty in oxide based ferroelectrics. Our belief that this is central to the understanding of ferroelectric behavior in these, the overwhelming majority of such materials, is based on earlier studies during the previous program.