Comparative study of ABO3 perovskite compounds.: 1.: ATiO3 (A = Ca, Sr, Ba, and Pb) perovskites

Comparative studies on the four ATiO(3) compounds are carried out to investigate the different ferroelectric behaviors of ATiO(3) on the basis of the experimental and theoretically optimized lattice structures. The stability predicted from the calculated total energies is in agreement with experimental observation. The obtained potential energy surfaces (PESs) show Ti displacements in CaTiO3 and SrTiO3 result in single-well potential whereas in BaTiO3 and PbTiO3 they produce double-well potential. In contrast to alkaline earth metal atoms, the PES of Pb displacement is double well. The calculated PIES supports the experimental conclusion that Ti displaces from [111] in tetragonal structure. In addition, the calculated hopping barriers are in agreement with the prediction of the vibronic theory. Charge distribution and the Ti-O and A-O bonding situation are analyzed on the basis of electronic structure calculations. It is shown that symmetry lowering enhances Ti-O covalent bonding in all the titled compounds and A-O bonds have some degree of covalency, with Pb-O being the strongest. Analyses show that there is a relationship between the charges on A and A-O interactions and the ferroelectric behaviors of the ATiO(3) perovskite compounds.