Browsing by Author "Hung, L.-W."
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Item Electric field- and temperature-induced phase transitions in high-strain relaxor-based ferroelectric Pb(Mg1/3Nb2/3)1-xTixO3 single crystals(2007-12-07) Chien, R.R.; Schmidt, V. Hugo; Tu, Chi-Shun; Wang, F.-T.; Shih, I.-C.; Hung, L.-W.; Luo, H.As a review, we compare results in electric-field- and temperature-induced phase transitions for four Pb(Mg1/3Nb2/3)1 - xTixO3(PMNT-x) single crystals, namely (001)-cut PMNT-x (x = 24%, 33%, and 40%) and (111)-cut PMNT-33%. Dielectric properties and domain states were measured as functions of temperature and electric field. The hysteresis loops of polarization versus electric field at room temperature were also measured. The intermediate monoclinic phases are essential in bridging higher symmetries while the electric-field- or temperature-induced transitions are taking place. Whether or not a monodomain state can be induced by a dc electric field strongly depends on crystallographic orientation, PbTiO3 content, and temperature.Item Field-induced polarization rotation in (001)-cut Pb(Mg1/3Nb2/3)0.76Ti0.24O3(2004-05-11) Chien, R.R.; Schmidt, V. Hugo; Tu, Chi-Shun; Hung, L.-W.; Lou, H.Polarization rotation of field-induced phase transformations was observed by means of a polarizing microscope on a (001)-cut single crystal Pb(Mg1/3Nb2/3)0.76Ti0.24O3 (PMNT24%) at room temperature with an electric field applied along the [001] direction. A hysteresis loop was also measured for comparison. As the electric field increases, polarizations of rhombohedral R domains rotate toward the [001] tetragonal T001 phase through MA-type monoclinic distortions, i.e., R⃗ MA→T001. The crystal cannot entirely reach the T001 phase as the field approaches 44 kV/cm. In addition, spotlike domains that perhaps correspond to MB-type monoclinic or triclinic phases were also observed. This field-induced phase transformation is strongly irreversible.Item Phase coexistence of temperature-dependent phase transformation in relaxor ferroelectric Pb(Mg1/3Nb2/3)1-xTixO3 single crystal(2004) Chien, R.R.; Schmidt, V. Hugo; Tu, Chi-Shun; Hung, L.-W.Coexistence of monoclinic and tetragonal domains is evidenced in a (001)-cut Pb(Mg1/3Nb2/3)0.61Ti0.39O3 (PMNT39%) single crystal from temperature dependent observation of domain structures and dielectric permittivity. The coexistence persists until the crystal transforms into the cubic phase near 455 K. As temperature increases, the monoclinic domains progressively transform to the tetragonal phase via polarization rotations of monoclinic distortions. This causes increasing volume of the tetragonal domain matrix as temperature increases before the cubic phase takes over.Item Temperature and E-field-dependent polarization rotations in (211)-cut Pb(Mg1/3Nb2/3)0.69Ti0.31O3 (PMNT31%) single crystal(2004) Tu, Chi-Shun; Hung, L.-W.; Chien, R.R.; Schmidt, V. HugoPolarization rotations of temperature- and electric-field-dependent phase transformations in a (211)-cut Pb(Mg1∕3Nb2∕3)0.69Ti0.31O3Pb(Mg1∕3Nb2∕3)0.69Ti0.31O3 (PMNT31%) single crystal were observed by means of polarizing microscopy. Dielectric permittivity was also measured as a function of temperature and frequency. Below 380 K domains are mostly rhombohedral (R)(R) phase mixed with monoclinic (M)(M) domains. As temperature increases above 380 K, polarizations of the rhombohedral domains begin to rotate toward the cubic (C)(C) phase through monoclinic distortions, i.e., R→M→CR→M→C, associated with a long-range percolation of monoclinic phase near 380 K. However, the tetragonal phase was not observed apparently. Electric-field-dependent domain structures show that a long-range R→MR→Mphase transformation takes place in the range of 3–5kV∕cm3–5kV∕cm as electric field increases. The crystal cannot reach a monodomain as the electric field reaches 26kV∕cm26kV∕cm. A hysteresis loop of polarization versus electric field was also measured for comparison with electric-field-dependent observation of polarizing microscopy.Item Temperature- and electric-field-dependent domain structures and phase transformations in (001)-cut tetragonal Pb(Mg1/3Nb2/3)1-xTixO3 (x=40) single crystal(2005) Chien, R.R.; Schmidt, V. Hugo; Hung, L.-W.; Tu, Chi-ShunTemperature- and electric (E)-field-dependent domain structures and phase transformations in a (001)-cut Pb(Mg1∕3Nb2∕3)0.6Ti0.4O3 (PMNT40%) single crystal have been investigated by polarizing microscopy and dielectric permittivity. The unpoled crystal has tetragonal phase domains (15–60μm wide) with polarizations along [100] and [010], which are separated by 90° domain walls. They coexist with a small fraction of the monoclinic phase domains near 200K. The tetragonal domains increase rapidly at the expense of the monoclinic domains as the temperature increases toward room temperature. This may account for the steplike dielectric anomaly in ε′ from around 280K. The whole crystal reaches the cubic phase near 464K. The E-field-dependent domain structures at room temperature show a significant change near 11kV∕cm when the polarizations rotate to the tetragonal [001] (T001) direction through the monoclinic phase. Microcrackings begin to develop near 12.5kV∕cm. The entire crystal becomes T001 monodomain near 33kV∕cm. After the E field is removed, the crystal does not reestablish the T100 and T010 macrodomains, but instead breaks up into tetragonal microdomains.