PRESSURE-INDUCED STRUCTURAL PHASE-TRANSITION OF CDS MICROCRYSTALS STUDIED BY RAMAN-SCATTERING

The effects of finite size on the pressure-induced structural phase tr ansition of CdS microcrystals have been studied by Raman scattering. B oth 1-LO and 2-LO phonon modes increased slowly in intensity and then diminished rapidly with an increase in pressure, indicating the occurr ence 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 elevat ion of the phase transition pressure for the CdS microcrystals prepare d by a break-down method was observed at much larger size than that fo r the CdS microcrystals produced by evaporation in Ar gas and embedded in SiO films. The observation is explained by the presence of remarka ble inhomogeneous strain in the former samples. It was also found that the samples with smaller particle size showed poorer recovery after b eing retrieved at 1 atm. We discuss the importance of inhomogeneous st rains as well as defects and surface condition in understanding the pr essure-induced structural phase transition in a finite system.