2004 Volume 45 Issue 7 Pages 2056-2061
The local electronic structures are simulated for a perovskite-type oxide with four polymorphous phases, SrZrO3, using the DV-Xα molecular orbital method. It is found that a series of phase transitions occurs at certain temperatures so as to retain not only the Zr-O bond strength, but also the Sr-O bond strength, by the tilting of ZrO6 octahedra and the attendant accommodation to the Zr-O and the Sr-O interionic distances. The occurrence of such smart phase transitions is observed in other perovskite-type oxides, SrRuO3 and SrHfO3. Another type of phase transition occurs by the cooperative ionic displacements along the  direction in BaTiO3. The differences in the local chemical bond are discussed between the two types of phase transitions.