NEUTRON AND SYNCHROTRON-RADIATION HIGH-PRESSURE EXPERIMENTS ON ALUMINATE SODALITE SR-8[AL12O24](CRO4)(2)

High pressure powder diffraction experiments were carried out on the a luminate sodalite Sr-8[Al12O24].(CrO4)(2) using a miniature clamped ce ll with neutron radiation at the ILL and a diamond anvil cell with syn chrotron radiation at Hasylab/Desy. The results of both experiments ag ree well. Lattice parameters were determined up to a pressure of 7.2 G Pa. The average linear compressibility amounts to 4.3 . 10(-3) GPa(-1) , which corresponds to a linear bulk modulus of 233 GPa. The observati on of superstructure reflections could be related to two new phase tra nsitions. The first one occurs between 0.37 and 0.5 GPa, the second on e at about 2.0 GPa. A final measurement at ambient pressure revealed t he reversible character of the pressure induced phase transitions.