Investigation of Crystal Structure of SrLa(FeTi)O6 and BaLa(FeTi)O6 Perovskites by Rietveld Refinement

TL;DR

This study revisits the crystal structures of SrLa(FeTi)O6 and BaLa(FeTi)O6 perovskites using Rietveld refinement, correcting previous misassignments and confirming their disordered structures in orthorhombic and cubic space groups.

Contribution

The paper provides a revised and accurate determination of the crystal structures of SrLa(FeTi)O6 and BaLa(FeTi)O6, correcting earlier reports of their symmetry and ordering.

Findings

SrLa(FeTi)O6 is orthorhombic in Pnma space group.

BaLa(FeTi)O6 is cubic in Pm3m space group.

Both compounds exhibit disordered cation occupancies.

Abstract

The structures of the recently reported ordered perovskites SrLa(FeTi)O6 and BaLa(FeTi)O6 have been revisited using Rietveld analysis of the powder x-ray diffraction data. Our studies clearly show that earlier authors have incorrectly reported the tetragonal structure in the I4/m space group for SrLa(FeTi)O6 and the cubic structure in the Fm3m space group for BaLa(FeTi)O6. The correct structure is found to be orthorhombic in the Pnma space group for SrLa(FeTi)O6 while cubic in the Pm3m space group for BaLa(FeTi)O6. Thus the BaLa(FeTi)O6 is not an ordered double perovskite as the occupancies of Ba/La ions at A-site and Fe/Ti ions at B-site are disordered resulting in the primitive cubic unit cell in the Pm3m space group. Similarly, the occupancies of Sr/La ions at A-site and Fe/Ti ions at B-site are disordered in SrLa(FeTi)O6 also, ruling out the ordered perovskite structure.