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

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 (100)(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). 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. (C) 2003 Elsevier B.V. All rights reserved.