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artículo con referato
"Electronic properties in intrinsically disordered double perovskites: Sr3MnMo2O9 and Ba3MnMo2O9 with Mo5+ valence state"
C.A. López, M.E. Saleta, J.C. Pedregosa, R.D. Sánchez, D.G. Lamas, J.A. Alonso and M.T. Fernández-Díaz
J. Alloy. Compd. 661 (2016) 411-418
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)º; whereas Ba3MnMo2O9 presents a cubic lattice, space group Fmm, 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.
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