Size-Dependence of Phase Transition of CdS Microcrystals

Abstract

We present experimental evidence which shows that the critical pressure (P c ) of the structural phase transition in CdS microcrystals under pressure differs from that of the bulk state and also that its magnitude depends on the microcrystal size. Far-infrared transmission measurements on CdS microcrystals of various sizes were carried out at pressure up to 8.3 GPa at room temperature by using synchrotron light source. The surface phonon at around 268 cm -1 at P=0 (atmosphere pressure) showed a blue shift with pressure. With further increase in pressure, the surface phonon showed a sudden decrease in energy. The very broad absorption band was found at the high pressure phase after the structural phase transition. Particle with smaller diameters was found to show higher P c values. The origin of the increase in the P c value is discussed related to thermodynamics and a surface tension of microcrystal.