Structural and magnetic properties of the perovskites A2LaFe2SbO9 (A = Ca, Sr, Ba)

Polycrystalline samples of A2LaFe2SbO9 (A ​= ​Ca, Sr, Ba) perovskites appeared monophasic to X-ray or neutron powder diffraction but a single-crystal study utilising transmission electron microscopy revealed a greater level of complexity. Although local charge balance is maintained, compositional and structural variations are present among and within the submicron-sized crystals. Despite the inhomogeneity, A ​= ​Ca is monophasic with a partially-ordered distribution of Fe3+ and Sb5+ cations across two crystallographically-distinct octahedral sites, i.e. Ca2La(Fe1.25Sb0.25)2d (Fe0.75Sb0.75)2cO9. For A ​= ​Sr or Ba, the inhomogeneities result in differences in the tilting patterns of the octahedra and the ordering of the B cations. Particles of A ​= ​Sr contain a phase (Fe:Sb ~2:1) without B cation ordering and one (Fe:Sb ~1:1) with B cation ordering. Monophasic A ​= ​Ba lacks long-range cation order although ordered nanodomains are present within the disordered phase. The temperature dependence of the magnetic properties of each sample is discussed.