Browsing by Author "Tseng, C.-T."

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Dielectric and photovoltaic phenomena in tungsten-doped Pb(Mg1/3Nb2/3)1-xTixO3 crystal
(2006) Tu, Chi-Shun; Wang, F.-T.; Chien, R.R.; Schmidt, V. Hugo; Tseng, C.-T.
This work investigates dielectric and photovoltaic behaviors in Pb(Mg1∕3Nb2∕3)0.64Ti0.36O3single crystaldoped with 0.5mol% WO3. Dielectric permittivities measured as functions of temperature and frequency reveal two first-order-type phase transitions upon heating and cooling. The photovoltaic response strongly depends on illumination wavelength, sample thickness, and prior electric-field poling. The relation of photovoltage and light intensity under near-ultraviolet (λ=406nm)illumination for the poled samples can be expressed by an exponential equation. Optical transmission reveals that the cutoff wavelength is near 400nm and indicates a minimum electronic energy gap of ∼3.0eV.
Dielectric/piezoelectric resonance in high-strain Pb(Mg1/3Nb2/3)1-xTixO3 crystals
(2005) Tu, Chi-Shun; Chien, R.R.; Schmidt, V. Hugo; Wang, F.-T.; Hsu, W.-T.; Tseng, C.-T.; Shih, C.C.
This work presents dielectricresonance in Pb(Mg1∕3Nb2∕3)1−xTixO3 crystals after electric (E)-field poling, which is crucial for piezoelectric applications. Dielectricpermittivity has been measured as functions of temperature, frequency, poling E-field strength, and Ti content (x=25% and 34%). Frequency-dependent dielectric spectroscopy after poling exhibits multiple piezoelectricresonances between 0.2 and 1MHz, and can be described by the forced-damped-oscillator model. The resonantspectra show significant changes while phase transitions are taking place.
Field-induced orientational percolation to a ferroelectric phase in relaxor Pb(In1/2Nb1/2)1-xTixO3
(2007-06-05) Tu, Chi-Shun; Chien, R.R.; Hung, C.-M.; Schmidt, V. Hugo; Wang, F.-T.; Tseng, C.-T.
This work presents direct observations of orientational percolation and depolarization in a (001)-cut relaxor Pb(In1∕2Nb1∕2)0.70Ti0.30O3 (PINT30%) crystal by means of dielectric permittivity, depolarization current, domain structure, and hysteresis loop. Electric (E)-field poling induced a 10–300μm size orientational percolation transition in the matrix. The percolation breaks down at depolarization temperature Td≅395K, which is ∼20–40K higher than in rhombohedral Pb(Mg1∕3Nb2∕3)1−xTixO3. Near 420K, the remaining polarization disappears, and the full relaxor-type dielectric dispersion due to polar nanoclusters reappears, and remains evident up to the Burns temperature TB≅520K. Under E=40kV∕cm at room temperature, small regions of [001] tetragonal domains appeared, but most of the crystal exhibited field-induced percolation rhombohedral and monoclinic microdomains embedded randomly in the matrix. This work suggests that this relaxor ferroelectric consists of two components (spherical glassy matrix and polar nanoclusters) as proposed for Pb(Mg1∕3Nb2∕3)O3 by Blinc et al. [Phys. Rev. Lett. 91, 247601 (2003)].
Nanotwin and phase transformation in tetragonal Pb(Fe1/2Nb1/2)1-xTixO3 single crystal
(2008) Tu, Chi-Shun; Tseng, C.-T.; Chien, R.R.; Schmidt, V. Hugo; Hsieh, C.-M.
This work is a study of phase transformation in (001)-cut Pb(Fe1/2Nb1/2)1−xTixO3Pb(Fe1/2Nb1/2)1−xTixO3 (x=48%)(x=48%) single crystals by means of dielectric permittivity, domain structure, and in situ x-ray diffraction. A first-order T(TNT)-C(TNT)T(TNT)-C(TNT) phase transition was observed at the Curie temperature TC≅518KTC≅518 K upon zero-field heating. T, TNTTNT, and C are tetragonal, tetragonal nanotwin, and cubic phases, respectively. T(TNT)T(TNT) and C(TNT)C(TNT) indicate that minor TNTTNT domains reside in the T and C matrices. Nanotwins, which can cause broad diffraction peak, remain above TC≅518KTC≅518 K and give an average microscopic cubic symmetry in the polarizing microscopy. Colossal dielectric permittivity (>104)(>104) was observed above room temperature with strong frequency dispersion. This study suggests that nanotwins can play an important role in relaxor ferroelectric crystals while phase transition takes place. The Fe ion is a potential candidate as a BB-site dopant for enhancing dielectric permittivity.