SYNTHESIS AND STRUCTURAL STUDY OF NATI2(PO4)3-NASN2(PO4)3 SOLID-SOLUTIONS .1. THE EFFECT OF COMPOSITION ON LATTICE-PARAMETERS

Compounds NaM2IV(PO4)3 with NZP-type structure present a different behavior depending on the nature of M(IV). For M(IV) = Ti and Zr the structure shows the space group R3cBAR. whereas for M(IV) = Sn the space group is R3BAR. Differences in behavior of NaTi2(PO4)3 - NaSn2(PO4)3 solid solutions are discussed in relation to the composition, The variation of the lattice parameters with composition in NaTi2-xSnx(PO4)3 (O < x < 2) solid solutions, prepared by ceramic method, has been studied. A sharp change in the lattice parameter "a" is observed between the compositions with x = 1 and 1.2. The lattice parameter "c" increases as the Sn content increases in the whole range of composition. The space group R3cBAR becomes to R3BAR for the composition with x > 1. The structure of the compound with x = 1 (NaSnTi(PO4)3) has been determined applying the Rietveld method to deconvolute the powder x-ray diffraction profile.