THEORETICAL-STUDY OF SPONTANEOUS POLARIZA TION AND BIREFRINGENCE IN THE FERROELECTRIC-TETRAGONAL PHASE OF BATIO3

Theoretical study of spontaneous polarization and birefringence in the ferroelectric-tetragonal phase of BaTiO3. The spontaneous polarizatio n in the tetragonal phase of BaTiO3 is calculated from a microscopic m odel taking into account of the electronic polarizabilities of the con stituent ions. The measured optical anisotropy of this compound can be explained by using the spontaneous Kerr effect due to the local field acting on the constituent ions of the lattice. Calculations show that the birefringence and the spontaneous polarization decrease with incr easing temperature in good agreement with the experimental data.