Physics and Chemistry of Minerals

, Volume 27, Issue 8, pp 583–589

Crystal chemistry of perovskite-type compounds in the tausonite-loparite series, (Sr1−2xNaxLax)TiO3

  • R. H. Mitchell
  • A. R. Chakhmouradian
  • P. M. Woodward
ORIGINAL PAPER

DOI: 10.1007/s002690000103

Cite this article as:
Mitchell, R., Chakhmouradian, A. & Woodward, P. Phys Chem Min (2000) 27: 583. doi:10.1007/s002690000103
  • 293 Downloads

Abstract

Perovskite-type compounds in the series tausonite-loparite, (Sr1−2xNaxLax)TiO3, were synthesized by solid-state reaction (final heating at 1200–1300 °C), and studied using “conventional” and synchrotron X-ray powder diffractometry. The structures of intermediate compositions were determined using the Rietveld profile refinement method. In the compositional range 0 ≤x ≤ 0.1, the series comprises perovskites characterized by an undistorted cubic structure (space group Pmm, a ≈ 3.905–3.902 Å, Z = 1). Intermediate compounds in the range 0.15 ≤ x ≤ 0.35 crystallize with tetragonal symmetry (I4/mcm, a ≈ \(\), c ≈ \(\), Z = 4) derived from the cubic aristotype by antiphase rotation of the TiO6 octahedra about a fourfold axis. The angle of rotation estimated from the positional parameters of oxygen atoms ranges from 2.5(7)° to 5.5(4)°. The cubic-to-tetragonal transition arises from substitution of Sr2+ by the comparatively smaller Na1+ and La3+ cations. A further transition from the tetragonal to rhombohedral symmetry (Rc, a ≈ \(\), c ≈ 2\(\), Z = 6) occurs between x = 0.35 and 0.40, and apparently does not involve formation of perovskite with an intermediate two-tilt structure (Imma). The rhombohedral structure is characterized by a multicomponent octahedral tilt about a threefold axis ranging in magnitude from 6.5(2)° to 7.7(2)°. In the series (Sr1−2xNaxLax)TiO3, the unit-cell dimensions decrease, and the degree of structural distortion increases with x.

Key words Perovskite Loparite Tausonite Structure 

Copyright information

© Springer-Verlag Berlin Heidelberg 2000

Authors and Affiliations

  • R. H. Mitchell
    • 1
  • A. R. Chakhmouradian
    • 1
  • P. M. Woodward
    • 2
  1. 1.Department of Geology, Lakehead University, 955 Oliver Road, Thunder Bay, Ontario P7B 5E1, Canada Tel.: +807-343 8329 Fax: +807-346 7853 e-mail: ACHAKHMO@gale.lakeheadu.caCA
  2. 2.Department of Chemistry, Ohio State University, 100 W 18th Avenue, Columbus, Ohio 43210-1185, USAUS

Personalised recommendations