The synthesis of reactive nitridation precursors prepared using citrate complexation/calcination route has shown interest in the study of the system R2Tasingle bondOsingle bondN. Novel fluorite-type phases have been evidenced in the oxide series R2TaO5.5 (R = Ndsingle bondYb, Y) and oxynitride series R2.67Ta1.33(O,N,□)8. Chemical and optical analyses were performed to characterize these phases, as well as structural analogies with R2WO6 and R2MoO5 oxide families.