SYNTHESIS AND PROPERTIES OF NITRITE NITRATE SODALITE SOLID-SOLUTIONS NA8[ALSIO4]6(NO2)2-X(NO3)X - 0.4-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-1.8

Nitrite-nitrate sodalite Na8[AlSiO4]6(NO2)2-x(NO3)x (0.4 ≤ x ≤ 1.8) solid solutions have been prepared using different methods: by hydrothermal synthesis in the presence of NaNO2 at temperatures between 770 and 970 K ("direct" preparation) and by high-temperature oxidation of previously synthesized nitrite sodalite in air ("indirect" preparation). Both methods yield sodalites, imbibing a maximal amount of 90% nitrate within their cages. The oxidation process is characterized by the continuous weight uptake of the crystals during heating as well as by a rising unit cell volume according X-ray powder diffraction studies. A temperature of 1050 K could be estimated as the favorable value for this reaction inside the sodalite cages. The properties of the members of the new solid solution series have been studied by simultaneous thermal analysis, high-temperature X-ray diffraction, and IR spectroscopy. A reversible expansion of the unit cell volume at temperatures ≥920 K indicates orientational disorder and a high degree of intracage dynamics of the nitrite and nitrate guest species. © 1991.