Crystal structure and magnetic properties of Ba${}_2{R}_{2\mathrm{/}3}$TeO${}_6$ ($R$ = Y, La, Pr, Nd, Sm-Lu) double perovskites

A new series of cubic double perovskites Ba${}_2{R}_{2\mathrm{/}3}$TeO${}_6$ ($R$ = Y, La, Pr, Nd, Sm-Lu) was synthesized via solid state reaction. The $R^{3+}$ and Te${}^{6+}$ 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) {\AA} for Ba${}_2$La${}_{2\mathrm{/}3}$TeO${}_6$ to a = 8.3310(4) {\AA} for Ba${}_2$Lu${}_{2\mathrm{/}3}$TeO${}_6$. 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. Ba${}_2$La${}_{2\mathrm{/}3}$TeO${}_6$, Ba${}_2$Y${}_{2\mathrm{/}3}$TeO${}_6$ and Ba${}_2$Lu${}_{2\mathrm{/}3}$TeO${}_6$ show primarily temperature-independent magnetic susceptibility due to the lack of a local rare earth moment. For Ba${}_2$Sm${}_{2\mathrm{/}3}$TeO${}_6$ and Ba${}_2$Eu${}_{2\mathrm{/}3}$TeO${}_6$, 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.