Electronic properties in intrinsically disordered double perovskites: Sr3MnMo2O9 and Ba3MnMo2O9 with Mo5+ valence state

Sr3MnMo2O9 and Ba3MnMo2O9 double perovskites with Mo5+ valence states have been prepared in polycrystalline form by thermal treatment, in reducing atmosphere (H2/N2 flow), of previously decomposed citrate precursors. These materials have been studied by X-ray and neutron powder diffraction (XRPD, NPD), magnetic and transport measurements. At room temperature, the crystal structure of Sr3MnMo2O9 is monoclinic, space group P21/n, with a = 5.6564(1) Å, b = 5.6383(1) Å, c = 7.9765(2) Å, β = 89.994(7) whereas Ba3MnMo2O9 presents a cubic lattice, space group Fm3¯ m, with a = 8.14900(8) Å. These samples present a frustrated magnetic interaction below to 12 and 9 K for Sr3MnMo2O9 and Ba3MnMo2O9, respectively. Semiconductor behaviour, observed either from d.c. or a.c. measurements, was modelled by a variable-range hopping mechanism. This transport behaviour is in accord with the electronic configurations Mn2+(3 d5)-Mo5+(4 d1) and supports the absence of mixed valence states in both double perovkites. Fil: Lopez, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Investigaciones en Tecnología Química. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Investigaciones en Tecnología Química; Argentina Fil: Saleta, Martin Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigación y Aplicaciones No Nucleares. Gerencia de Física. Laboratorio de Resonancias Magnéticas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Universidad Nacional de Cuyo; Argentina