6 . -Nanocrystals (20-50 nm) of the title compound are prepared by an auto-ignition combustion process from an aqueous solution of precursors obtained from a mixture of Tm2O3, Ba(NO3)2, Sb2O3, and nitric, tartaric, and citric acid. The polycrystalline combustion product is sintered to about 97% density at about 1450°C for 4 h.