A Structural Study of the Perovskite Series Na1/2+xLa1/2−3xTh2xTiO3

✍ Scribed by Roger H. Mitchell; Anton R. Chakhmouradian

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 294 KB
• Volume: 138
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1998.7789

✦ Synopsis

An X-ray powder diffraction study of the series Na 1/ 2؉x La 1/ 2؊3x Th 2x TiO 3 is presented. The series comprises orthorhombic CaTiO 3 -type perovskites (Pnma, a+c+(2 a p , b+2 a p ) in the range 04x40.083 and tetragonal La 1/2 Li 1/2 TiO 3 -type perovskites (P4/mmm, a ‫؍‬ a p , c+2a p ) in the range 0.1004x4 0.167. The structure of the orthorhombic members is derived from the cubic aristotype by octahedral rotation. The degree of octahedral rotation is relatively small ( ‫؍‬ 4.1-7.6°), compared to that of other CaTiO 3 -type perovskites. The tetragonal members of the series exhibit partial ordering of the cations at the A-site: the 1a and 1b sites are preferentially occupied by Na and Th, respectively. This results in alternate layers of Na and Th atoms perpendicular to the c axis of the tetragonal cell. Ti atoms are displaced from the center of the TiO 6 polyhedra due to the strong electrostatic repulsion effect of Th and La at the A-site. In contrast to previous studies, the end-member Na 2/3 Th 1/3 TiO 3 is shown not to have a cubic cell.