High-pressure Raman study on nanocrystalline CeO2

To evaluate the reported change in the physical and electronic properties o f nanomaterials as compared to bulk material, we performed high-pressure Ra man spectroscopy on nanocrystalline CeO2 at room temperature up to a pressu re of 36 gigapascals (GPa) with and without pressure medium. We observed a linear dependence of the first order Raman signal on pressure. The compress ion and decompression follow the same path under hydrostatic conditions but show hysteresis (similar to 20 R cm(-1)) under nonhydrostatic compression and decompression. We found that fluorite type CeO2 undergoes a phase trans ition to an orthorhombic PbCl2 type structure at a pressure around 26.5 GPa , which is less than that reported for bulk CeO2 (32 GPa). On decompression , we found that the high-pressure phase can exist down to a pressure of 1.8 GPa. The results obtained on compression of sample with CsCl as the pressu re medium were compared to that compressed without any medium. (C) 2001 Ame rican Institute of Physics.