Manganese sites and valence states in RCu3-xMn 4+xO12(R = Ca or La) magnetoresistive perovskites

The manganese environment has been investigated by X-ray Absorption Spectroscopy (XAS) in RCu3-xMn4+xO12(R = Ca or La) magnetoresistive perovskites. The analysis of the data evidence the presence of two different Mn edges, each one related with the two different sites in which Mn can be located. Mn-O distances at both sublattices were obtained by Extended X-ray Absorption Fine Structure (EXAFS) analysis. The variation of the threshold energy corresponding to the Mn at A sites is driven by the changes in the Mn-O distances. On the contrary, the edge of Mn at Mn-O6 sites, which is equivalent to the one observed in manganites, is dominated by the change in its valence. The results suggest that electrical conduction in this series of compounds is due to the Mn eg electrons at B site (mixed valence Mn) and not to the localized electrons from Mn at A site of the perovskite. © Physica Scripta 2005