SIZE EFFECT ON THE RAMAN-SPECTRA AND PHASE-TRANSITION IN PBZR0.2TI0.8O3 NANOCRYSTALLINE POWDERS

We report a size effect on the Raman spectra of and the phase transiti on in PbZr0.2Ti0.8O3 nanocrystalline powders. The samples were synthes ized by the stearic acid gel method. The average grain sizes and cryst al structures were determined by X-ray diffraction. The Raman spectra of PbZr0.2Ti0.8O3 nanocrystals have been measured under different temp eratures and hydrostatic pressures. The results show that the phase tr ansition temperature T-c shifts to a lower temperature with decreasing grain size. The possibility that the additional band occurring in the low frequency Raman spectra might be due to zone boundary transverse acoustical phonons which couple to the q approximate to 0 soft E (tran sverse optical) mode is confirmed. The Raman spectra, as a function of pressure, reveal that the phase transition may be connected with a di ffuse phase transition.