Structural phase transition of CdS microcrystals embedded in glassy matrix under high pressure

CdS microcrystals of various sizes embedded in a germanium dioxide glass matrix have been studied by Raman scattering and optical absorption under high pressure up to about 9 GPa. Structural phase transition of the CdS microcrystals from wurtzite to rock salt phase was observed at a pressure higher than 6 GPa, which is far above the bulk CdS transition pressure of 2.7 GPa. Under a pressure higher than 6 GPa, the 1-LO Raman intensity of the wurtzite phase of CdS microcrystals decreases gradually with time. After the pressure is released from about 9 GPa to atmospheric pressure, the high pressure rock salt phase is preserved at room temperature. We found that CdS microcrystals of the rock salt phase recovered to the wurtzite phase by temperature annealing at atmospheric pressure. Our observations suggest that the matrix plays an important role.