INFLUENCE OF GRAIN-SIZE ON THE SOFT MODE AND THE PHASE-TRANSITION IN THE NANOCRYSTALLINE PBTI1-XZRXO3 SYSTEM

The Raman spectra of nanocrystalline PbTi0.75Zr0.25O3 show that its pe rovskite phase occurred at a higher crystallization temperature during its sol-gel process than the perovskite PbTiO3 phase. The effects of grain size on the ferroelectric phase transition and the soft mode hav e been investigated. The phase transition temperature T(c) is shifted to a lower temperature with decreasing grain size. The possibility tha t the additional mode occurring in the low frequency Raman spectra mig ht be due to zone boundary transverse acoustical phonons which couple to the q approximately 0 soft TO phonon mode is confirmed. The Raman s pectra, as a function of pressure, reveal that the phase transition ma y be correlated with Diffuse Phase Transition (DPT).