Crystal structure and magnetic properties of Ba2R2/3TeO6 (R = Y, La, Pr, Nd, Sm-Lu) double perovskites

A new series of cubic double perovskites Ba2R2/3TeO6 (R = Y, La, Pr, Nd, Sm-Lu) was synthesized via solid state reaction. The R3+ and Te6+ ions are ordered on alternating octahedral sites, with the rare earth sites 2/3 occupied to balance the charge. The lattice parameters decrease monotonically from a = 8.5533(3) angstrom for Ba2La2/3 TeO6 to a = 8.3310(4) angstrom for Ba2Lu2/3TeO6. The lattice parameter for R = Y is close to that of Ho. Analysis of the resulting bond lengths indicates a structural relaxation around the R ion site. Ba2La2/3TeO6, Ba2Y2/3TeO6 and Ba2Lu2/3TeO6 show primarily temperature-independent magnetic susceptibility due to the lack of a local rare earth moment. For Ba2Sm2/3TeO6 and Ba2Eu2/3 TeO6, the susceptibilities are influenced by Van Vleck-like contributions from excited state multiplets. For the remaining members, the Curie-Weiss law is followed with low-temperature deviations that can be associated with various degrees of crystalline electric field splitting. No magnetic ordering was observed down to 1.8 K in any of the compounds.