| Summary: | 碩士 === 輔仁大學 === 物理學系 === 88 === Abstract
The longitudinal Brillouin back-scattering spectra and dielectric permittivities have been measured as a function of temperature in relaxor ferroelectric crystal (Pb(Mg1/3Nb2/3)O3) 1-x(PbTiO3)x (PMN-xPT：x=0.24, 0.32, 0.31 and 0.33), and (Pb(Zn1/3Nb2/3)O3)1-x(PbTiO3)x (PZN-xPT：x=0.085 and 0.095). These crystals have successive phase transitions (beside PMN- 24%PT). A sharp ferroelectric phase transition which is associated with a minimum in phonon frequency and an abrupt change in polarization, was observed in the high tempre- ature region (above 400 K). As temperature decreases, a diffuse phase transition which is associated with a broad frequency dependent dielectric spectrum and a gradual evolution in polarization. In addition, the nature of the thermal hysteresis for the dielectric permittivity confirms that these transition are first-order (high-temperature phase transition) and diffuse first-order (low-temperature diffuse phase transition), respectively.
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