Y. Koyama

Features of structural phase transition in La1−xSrFeO3

Abstract The structural phase transition in the insulating phase of La 1− x Sr x FeO 3 has been examined by X-ray powder diffraction. Based on the Rietveld analysis of the obtained profiles, the R 3 c – Pbnm structural transition was confirmed to take place in this oxide system. The interesting feature of the transition is that it is characterized by the appearance of the antiferroelectric displacement of the La/Sr atom, in addition to the change in the rotational–displacement pattern, R 25 x + R 25 y + R 25 z → R 25 x + R 25 y + M 3 z . It is thus understood that the low-temperature Pbnm phase can be identified as an antiferroelectric phase in oxides having a simple perovskite structure.

Crystallographic features of RTiO3 (R: Rare-earth ion)

Abstract The crystallographic features of the simple perovskite oxides RTiO3 with R=La, Nd, Sm and Y, which are known to be correlated-electron insulators, have been examined mainly at room temperature by transmission electron microscopy. Electron diffraction patterns indicated that the oxides with R=La and Nd have the space group Pbnm. In electron diffraction patterns of SmTiO3 and YTiO3, on the other hand, the twin splitting of reflections due to the Pbnm structure is seen along one of the 〈1 0 0〉 c directions, where the subscript c denotes the cubic Brillouin zone. That is, it is understood that their crystal system is lowered from an orthorhombic one to a monoclinic one. The analysis of the patterns also suggested that the Jahn–Teller atomic displacement with q =〈 1 2 1 2 0〉 c should be involved in the crystal structure for R=Sm and Y, in addition to the full symmetric Jahn–Teller lattice distortion in the structure for R=La and Nd.

Crystallographic Features of Ferroelectric Domain Structures in (Sr1-xBax)Bi2Ta2O9

The crystallographic features of the ferroelectric domain structures in (Sr1-xBax)Bi2Ta2O9 single crystals have been examined by transmission electron microscopy. The unique 90° domain structures were found in these single crystals. In SrBi2Ta2O9 with x = 0, particularly the majority domains with the ±[1 1 0]t polarization vectors in the tetragonal notation are divided by the minority ones with the vectors, which were observed as a curved-line contrast in dark field images.