Nasicon solid solution Na1+xZr2-xMx(PO4)3 (M = Y, Yb, or In) was prepared by solid-state reaction. The change of lattice parameter with changing x was determine and explained from the point of view of crystal chem. Nasicon solid solution can also be for prepared by the substitution of trivalent ions (Y3+, Yb3+, In3+) or bivalent Mg2+ for Zr4+ ion in Na3Zr2Si2PO12. At the same time, the high-temp. rhombohedral phase (space group R3c) is stabilized at room temperature Therefore, the monoclinic J rhombohedral phase transition at ~150?disappears. The condition of stabilizing the high-temp. phase is discussed.

Key words: STABILITY, CRYSTAL STRUCTURE DETERMINATION, SODIUM COMPOUNDS, SILICON COMPOUNDS, SOLID SOLUTION, SPACE GROUPS, SOLID PHASE REACTION, ZIRCONIUM COMPOUNDS, SODIUM PHOSPHORATE, THREE-DIMENSIONAL