Abstract :
Neutron and X-ray high-pressure powder-diffraction experiments on silica sodalite with 1,3-dioxolane as a template molecule, (C3H6O2)2[Si12O24], were performed up to a maximum pressure of 2.7 GPa. A phase transition from the fully expanded structure at ambient pressure, space group Im3̄m, to the acentric space group I4̄3m was derived from the observed compression behaviour. A ferro-elastic phase transition appears at about 1.2 GPa to the rhombohedral crystal system. From symmetry analysis and the observed transition behaviour the space groups R3 or R3m are proposed for p>1.2 GPa.
