INVESTIGATION OF CANCRINITE STRUCTURES BY POWDER NEUTRON DIFFRACTION

摘要

Deuterated forms of cancrinite, [Na_8(CO_3).(D_2O)_n] [AlSiO_4]_6 - CAN, and intermediate phase mixed disordered cancrinite-sodalite [Na_(8-y)(CO_3)_(1-y/2).(D_2O)_n] [AlSiO_4]_6 - CAN/SOD, have been synthesised and studied using variable temperature, high resolution powder neutron diffraction. The structure of cancrinite shows anions are present only in the main 12-membered ring channels, with water molecules co-ordinating to sodium in the 11-hedral s-cages. In situ, powder neutron diffraction, studies of the thermal decomposition of cancrinite and the disordered cancrinite/sodalite show marked differences in their behaviours. Both materials undergo a lattice contraction as water is lost between 100 and 300 ℃ though this process, and decomposition of the aluminosilicate framework, occur at significantly lower temperatures for the disordered structure.