Isomorphism in Crystalline Phosphates of the NaZr2(PO4)3 Structural Type and Radiochemical Problems

The problems of isomorphism in phosphates that are structural analogs of sodium zirconiumorthophosphate NaZr₂(PO₄)₃ (NZP) are discussed. Data on the crystal chemistry of orthophosphates of theframework structure are systematized according to the suggested classification of their formula types. Thetheoretically possible, actually occurring isomorphism of cations in phosphates, in particular, isomorphisminvolving f-element cations, is discussed. The isomorphous capacity of the NZP structure toward variouscations was evaluated. Data on isomorphism in phosphates are necessary for choosing a suitable single-phase ceramic matrix for incorporation of radionuclides and adjusting its composition to actual nuclear waste.