HYDROTHERMAL SYNTHESIS AND RECRYSTALLIZATION OF COMPOUNDS BELONGING TO THE NASICON FAMILY - SYNTHESIS AND CRYSTALLIZATION OF NA4ZR2SI3O12

Compounds of the Nasicon family have been prepared by a hydrothermal method in order to obtain single crystals adapted to polarized Raman studies. Reactant products may be oxides as well as silicates. The conditions for obtaining pure Na//4Zr//2Si//3O//1//2 are: (i) the ZrO//2/SiO//2 molar ratio must be equal to 2/3, (ii) Na//2O which must be in large excess, has to be introduced via NaOH solutions containing more than 30% of sodium hydroxide in weight, (iii) for pressures (P) higher than 400 bar the temperatures (T degree ) must be higher than 330 degree C. Single crystals of (0. 5 mm) have been obtained within ten days, for T equals 450 degree C and P higher than 400 bar.