HYDROTHERMAL SYNTHESIS AND CHARACTERIZATION OF NITRITE SODALITE SINGLE-CRYSTALS

Single crystals of nitrite sodalite Na8[AlSiO4]6(NO2)2 prepared hydrothermally at 570 K and 0.1 GPa show cubic symmetry (a0 = 8.931(2) angstrom) and complete ordering of the framework T atoms (SG P4BAR3n). The thermal properties have been characterized by simultaneous thermal analysis (TG, DTG, DTA) and high temperature X-ray powder diffraction. Heating in air yields a nitrite/nitrate sodalite according to the oxidation of the enclosed salt molecules. This intra-cage reaction is characterized by IR spectroscopy and thermogravimetry under open system conditions. Additional X-ray powder diffraction data (Guinier-Simon heating technique) indicate an expansion of the sodalite framework during this formation of nitrate within the beta-cages at 1000 K. The thermal decomposition of nitrite sodalite in an inert atmosphere (argon) occurs in the 950-1100 K interval, yielding a stuffed carnegieite phase.