Synthesis and structure determination of ferromagnetic semiconductors LaAMnSnO6 (A = Sr, Ba)

Abstract

LaAMnSnO₆ (A = Sr, Ba) have been synthesized by high temperature solid-state reactions under dynamic 1% H₂/Ar flow. Rietveld refinements on room temperature powder X-ray diffraction data indicate that LaSrMnSnO₆ crystallizes in the GdFeO₃-structure, with space groupPnma and, combined with transmission electron microscopy, LaBaMnSnO₆ in Imma. Both space groups are common in disordered double-perovskites. The Mn³⁺ and Sn⁴⁺ ions whose valence states were confirmed by X-ray absorption spectroscopy, are completely disordered over the B-sites and the BO₆ octahedra are slightly distorted. LaAMnSnO₆ are ferromagnetic semiconductors with a T_C = 83 K for the Sr- and 66 K for the Ba-compound. The title compounds, together with the previously reported LaCaMnSnO₆ provide an interesting example of progression from Pnma to Imma as the tolerance factor increases. An analysis of the relationship between space group and tolerance factor for the series LaAMnMO₆ (A = Ca, Sr, Ba; M = Sn, Ru) provides a better understanding of the symmetry determination for double perovskites.