Cubic Trisodium Phosphate

The sodium cations in the high-temperature cubic y form of Na3P04 can be replaced by one quarter of their number of Zf + to give crystals of composition Na9 j2t3,(P04)3 up to a limit of y = 0.5. 

The resulting vacancies are randomly distributed over the Na sites, but at lower temperatures the Zr atoms adopt ordered positions. Further replacement of Na+ by Zr leads to a different structure at y = 2, that is, rhombohedral NaZr2(P04)3 (see above) [60,61]. 

Anionic substitution can be made in Na3P04 to give solid solutions of the type Na3 (P04), (S04). These solid solutions have enhanced ionic conductivities which are associated with the increase in the number of Na lattice vacancies (cf. Nasicon). 

The ionic conduction of y-Na3P04 can be affected not only by doping with Zr, but with many other elements such as Hf, Ti, Sn, Ce, Th, Mg, Ca, Sr, Zn and Al. In compositions of the type Na3 3 A1 P04, the Na+ ions in the Na3P04 structure are replaced by AF+ and vacancies [62-64]. 

---