| Summary: | 碩士 === 輔仁大學 === 物理學系 === 96 === Abstract
Phase transformations of the (111)-cut Pb(Mg1/3Nb2/3)0.70Ti0.30O3 single crystals before and after an electric E-field poling have been investigated by means of dielectric permittivity, hysteresis loop, polarization current, and in situ x-ray diffraction as a function of temperature.
An R-T-C transition sequence was observed in the unpoled sample upon zero-field heating. R, T, and C are rhombohedral, tetragonal, and cubic phases, respectively. After a prior E-field poling, an extra intermediate monoclinic (possible MA) phase was induced and the crystal underwent an R-MA-T-C phase sequence with significant responses in polarization current. The dielectric dispersion was diminished after poling and reappeared in the cubic state. The dielectric permittivities with and without a prior poling were found to follow the Curie-Weiss equation, =C/(T-To), above the Burns temperature 505 K with the same Curie-Weiss constant C=1.9´105 K and Curie-Weiss temperature To=460 K.
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