Modification of Local Electronic Structures Due to Phase Transition in Perovskite-Type Oxides, SrBO<SUB>3</SUB> (B=Zr, Ru, Hf)

Abstract

The local electronic structures are simulated for a perovskite-type oxide with four polymorphous phases, SrZrO 3 , using the DV-X 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 ZrO 6 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, SrRuO 3 and SrHfO 3 . Another type of phase transition occurs by the cooperative ionic displacements along the [100] direction in BaTiO 3 . The differences in the local chemical bond are discussed between the two types of phase transitions.

Local Electronic Structure and Protonic Conductivity in Perovskite-Type Oxide, SrZrO<SUB>3</SUB>

“…40) The lattice parameters used are the same values as in bulk, a ¼ 0:58151 nm, b ¼ 0:81960 nm, c ¼ 0:57862 nm. According to our previous calculations, 41) the calculated electronic structure is not sensitive to the slight lattice parameter change with temperatures in this oxide. So, the calculated ionicities and bond orders are supposed to be less dependent on the tempareture.…”

Energy expression of the chemical bond between atoms in metal oxides

“…The other two examples, SrTiO 3 [19] and SrZrO 3 [19], are shown in Fig. 12(a) and (b), respectively.…”

“…The minimum Zr-O interatomic distance in cubic SrZrO 3 at 1443 K is close to the shortest Zr-O interatomic distance in pure ZrO 2 , so that the phase transition (i.e., the tilting of ZrO 6 octahedron) occurs around 1443 K, and the attendant increase in the Zr-O interatomic distance works to retain the Zr-O bond strength. Unless such a tilting does take place, the Zr-O bond will become very weak according to a hypothetical calculation [19]. by the transition from cubic to tetragonal phase.…”

“…According to our previous study [19], in the case of SrZrO 3 , the average Zr-O interatomic distance increases by tilting or rotation of ZrO 6 octahedron, and the average Zr-O bond strength is recovered to some extent by forming a distorted ZrO 6 octahedron by the phase transition [19]. The minimum Zr-O interatomic distance in cubic SrZrO 3 at 1443 K is close to the shortest Zr-O interatomic distance in pure ZrO 2 , so that the phase transition (i.e., the tilting of ZrO 6 octahedron) occurs around 1443 K, and the attendant increase in the Zr-O interatomic distance works to retain the Zr-O bond strength.…”

“…Such structural stability has been treated by total energy calculations [14][15][16]. Also, the calculations of phonon modes [17,18] and the Mulliken population analysis [19] have been performed to understand the phase transition. Besides these transitions, there is another phase transition from the perovskite to the post-perovskite in MgSiO 3 above 120 GPa and 2000 K [20].…”