Pressure-induced structural phase transition of CdS microcrystals studied by raman scattering

Abstract

The effects of finite size on the pressure-induced structural phase transition of CdS microcrystals have been studied by Raman scattering. Both 1-LO and 2-LO phonon modes increased slowly in intensity and then diminished rapidly with an increase in pressure, indicating the occurrence of the structural phase transition from a wurtzite to a rock salt phase. The pressure at which the structural phase transition occurred was found to be elevated gradually from 2.7 GPa (the phase transition pressure of bulk) as the particle size decreases. However, the elevation of the phase transition pressure for the CdS microcrystals prepared by a break-down method was observed at much larger size than that for the CdS microcrystals produced by evaporation in Ar gas and embedded in SiO films. The observation is explained by the presence of remarkable inhomogeneous strain in the former samples. It was also found that the samples with smaller particle size showed poorer recovery after being retrieved at 1 atm. We discuss the importance of inhomogeneous strains as well as defects and surface condition in understanding the pressure-induced structural phase transition in a finite system.