Synthesis, structure and ionic conductivity in nitrite sodalites

Abstract

Nitrite sodalite [Na₈(AlSiO₄)₆(NO₂)₂·xH₂O] has been synthsised by precipition from an aluminosilicate solution, and a series of cation-exchange reaction with silver have been carried out on this parent compound so as to obtain materials of general stoichiometry [Ag_yNa_{8 –y}(AlSiO₄)₆(NO₂)₂·xH₂O] where 0 < y < 8 and x≈ 2. The effects of substituting silver for sodium have been studied using powder X-ray diffraction, IR spectroscopy, ²⁹Si magic angle spinning NMR, and thermogravimetric analysis. Results indicate that substitution of sodium by silver leads to reorientation of the nitrite ion within the cage. Ionic conductivity has been characterised in two of these compounds using a.c. conductivity methods; at 500°C typical cation conductivities are in the range 10^–5–10^–4Ω^–1 cm^–1 with the fastest ion conduction observed with partial substitution of silver for sodium.