Synthesis and structure of new pyrochlore-type oxides Ln_2ScNbO_7 (Ln = Pr, Nd, Eu, Gd, Dy)

摘要

We report the synthesis and structural study of mixed oxides in the Ln_2ScNbO_7 series. New phases with Ln=Pr, Eu, Gd and Dy are obtained. All crystallize in the cubic pyrochlore structure type, space group F-d3m, with no Sc-Nb ordering on the B site. The structures are determined by Rietveld refinement. The evolution of cell parameters, interatomic distances and angles as a function of lanthanide cation size is discussed. Magnetic measurements show the absence of ordering down to 2 K, in agreement with the presence of strong geometric frustration in the lanthanide sublattice. The europium phase shows a peculiar magnetic behaviour; its magnetic susceptibility becomes constant below ca 50 K. This feature confirms the behaviour observed previously on Eu_2Ti_2O_7 and is ascribed to crystal field effects.