High oxygen pressure preparation, structural refinement, and thermal behavior of RMn(2)O(5) (R=La, Pr, Nd, Sm, Eu)

The title compounds have been prepared in powder form by a citrate technique followed by a high oxygen pressure (P= 200 bar) treatment. The La and Pr compounds are described for the first time. X-ray powder diffraction data are given, as well as the results of the Rietveld analysis of the patterns. All the phases are isostructural (space group Pbam), containing in the crystal structure infinite chains of Mn4+O6 octahedra sharing edges, linked together by Mn3+O5 and RO(8) units. All the studied compounds are electrical insulators. The thermal analysis of the samples enabled us to determine the oxidation state of Mn, which is slightly higher than expected, suggesting the presence of some oxygen excess in the structure. (C) 1997 Academic Press.