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

C.A. LOPEZ; M.E. SALETA; J.C. PEDREGOSA; R.D. SÁNCHEZ; D.G. LAMAS; J.A. ALONSO; M.T. FERNÁNDEZ-DÍAZ

JOURNAL OF ALLOYS AND COMPOUNDS

ELSEVIER SCIENCE SA

Lugar: Amsterdam; Año: 2016 vol. 661 p. 411 - 418

0925-8388

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, beta = 89.994(7)°; whereas Ba3MnMo2O9 presents a cubic lattice, space group Fm-3m, 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+(3d5)-Mo5+(4d1) and supports the absence of mixed valence states in both double perovkites.