| Summary: | 碩士 === 輔仁大學 === 物理學系 === 96 === This work is to investigate thermal effect and electric (E)-field poling effect in a (001)-cut Pb(Mg1/3Nb2/3)0.70Ti0.30O3 single crystal. The thermal effect was studied before and after electric field poling by means of dielectric permittivity, hysteresis loop, domain structure, polarization current, and x-ray diffraction. An R(RNT)-R(RNT)/T(TNT)-T(TNT)-C transition sequence was observed upon heating in the unpoled sample. After a prior E-field poling, an R(RNT)-T(TNT)-C phase sequence takes place upon heating. R, RNT, T, TNT, and C are rhombohedral, rhombohedral nanotwin, tetragonal, tetragonal nanotwin, and cubic phases, respectively. R/T indicates a coexistence of R and T phases. R(RNT) and T(TNT) indicates that RNT and TNT structures mimic monoclinic phases in the R and T matrices, respectively.
Electric-field dependent studies at room temperature by means of domain structure and x-ray diffraction were also carried out. Under E=38 kV/cm, T[001] domains appeared randomly in the matrix, suggesting that the matrix consists of dipole glass and ferroelectric nanoclusters. From the electric-field dependent x-ray diffraction experiment, the converse piezoelectric constant d33C, was calculated and compared with the data obtained from the conventional method measured by the d33 meter. It shows the same tendency with the results obtained from E-field dependent x-ray diffraction. The different mechanism causes different values of normal/converse piezoelectric constants.
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