Synthesis, Crystal and Magnetic Structure of the Double Perovskites A2NiMoO6 (A = Sr, Ba): A Neutron Diffraction Study

Abstract

AbstractA2NiMoO6 (A = Sr, Ba) perovskites have been prepared in polycrystalline form by thermal treatment, in air, of previously decomposed citrate precursors. These materials have been studied by X‐ray (XRD) and neutron powder diffraction (NPD) data. At room temperature, the crystal structure is tetragonal, space group I4/m, for Sr2NiMoO6 and for Ba2NiMoO6 the crystal structure is cubic, space group Fm$\bar 3$ m. Both perovskites contain divalent Ni cations. The low temperature antiferromagnetic ordering has been followed from sequential neutron diffraction data. Peaks of magnetic origin appear in the NPD patterns below temperatures of TN = 81.2 K and TN = 64.3 K for the Sr and Ba compounds, respectively. The magnetic structures are defined by a propagation vector k = (1/2,0,1/2) for Sr2NiMoO6 and k = (1/2,1/2,1/2) for Ba2NiMoO6. The refined magnitude of the Ni magnetic moments also suggests a divalent oxidation state with S = 1. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)