Structural evolution of the double perovskites Sr2B?UO6 (B? = Mn, Fe, Co, Ni, Zn) upon reduction. Magnetic behavior of the uranium cations

R. M. PINACCA; M. C. VIOLA; J. C. PEDREGOSA; R. E. CARBONIO; M. J. MARTÍNEZ LOPE; J. A. ALONSO

MATERIALS RESEARCH BULLETIN

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2011 vol. 46 p. 1755 - 1760

0025-5408

We describe the preparation of five perovskite oxides obtained upon reduction of Sr2B0UO6 (B' =Mn, Fe, Co, Ni, Zn) with H2/N2 (5%/95%) at 900oC during 8 h, and their structural characterization by X-ray powder diffraction (XRPD). During the reduction process there is a partial segregation of the elemental metal when B'= Co, Ni, Fe, and the corresponding B'O oxide when B'= Mn, Zn. Whereas the parent, oxygen stoichiometric double perovskites Sr2B'UO6 are long-range ordered concerning B' and U cations. The crystal structures of the reduced phases, SrB'0.5-xU0.5+xO3 with 0.37< x <0.27, correspond to simple, disordered perovskites; they are orthorhombic, space group Pnma (No. 62), with a full cationic disorder at the B site. Magnetic measurements performed on the phase with B'= Zn, indicate uncompensated antiferromagnetic ordering of the U5+/U4+ sublattice below 30 K.