Scholarly Work - Physics
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/3458
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Item Direct observation of ferroelectric domains and phases in (001)-cut Pb(Mg1/3Nb2/3)1-xTixO3 single crystals(2006) Chien, R. R.; Schmidt, V. Hugo; Tu, Chi-Shun; Wang, F.-T.Real-time direct observation of ferroelectric domains and phases under electric-field poling along [0 0 1] at room temperature in Pb(Mg1/3Nb2/3)0.67Ti0.33O3 (PMNT33%) single crystal has been performed by polarizing microscopy. A hysteresis loop of polarization vs. electric field at room temperature was also measured for comparison. By using relations of crystallographic symmetry and optical extinction, polarizing microscopy reveals orientations of the domain polarizations and their corresponding phases. It also provides direct real-time observation of microcracking phenomena. It was found that the monoclinic phase domains play a crucial role in bridging higher symmetry (tetragonal and rhombohedral) phases while field-induced phase transitions take place.Item Electric-field-induced and temperature‑induced phase transitions in high-strain ferroelectric Pb(Mg1/3Nb2/3)0.67Ti0.33O3 single crystal(2006) Chien, R. R.; Tu, Chi-Shun; Schmidt, V. Hugo; Wang, F.-T.This work is to study electric (E)-field-induced and temperature-induced phase transitions in (001)-cut Pb(Mg1/3Nb2/3)0.67Ti0.33O3 (PMNT33%) single crystal, which are critical concerns for piezoelectric applications. Dielectric properties and domain structures (by polarizing microscope) are measured as functions of temperature and E field. The hysteresis loop of the polarization versus E field at room temperature is also measured. Without any E-field application, upon heating a first-order-type phase transition sequence rhombohedral (R) → rhombohedral/monoclinic/[001]tetragonal (R/M/T001) → cubic (C) takes place near 350 and 430 K, respectively. Under a dc E-field application along [001] at room temperature, [001] tetragonal (T001) phase domains are induced by various phase transition sequences, i.e. R → T001,R → M → T001, R → T → T001,andR→ M → T → T001,asthe E-field strength increases. In addition, E-field-induced microcracking is observed in this work.Item Nanotwins and phases in high-strain Pb(Mg1/3Nb2/3)1-xTixO3 crystal(2008) Tu, Chi-Shun; Hsieh, C.-M.; Chien, R.R.; Schmidt, V. Hugo; Wang, F.-T.; Chang, W.S.This work is a study of the thermal stability of (001)-cut Pb(Mg1/3Nb2/3)1−xTixO3 (x=0.30) single crystals before and after an electric (E)-field poling by means of dielectricpermittivity, 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. R, RNT, T, TNT, and C are the rhombohedral, rhombohedral nanotwin, tetragonal, tetragonal nanotwin, and cubic phases, respectively. R/T indicates coexistence of the R and T phases. R(RNT) and T(TNT) indicate that the RNT and TNTstructures mimic monoclinic phases in the R and T matrices, respectively. After a prior E-field poling, an R(RNT)-T(TNT)-C phase sequence takes place upon heating. The dielectricpermittivity and current density evidenced an additional polarization at 355 K, which is associated with the vanishing of the dielectric dispersion, which reappears near 410 K and remains up to the Burns temperature TB=510 K. This study suggests that nanotwins (RNT and TNT) can play an important role in high-strain piezoelectric crystals while phase transition takes place. Under E=38 kV/cm, [001] T domains randomly appeared in the matrix, suggesting that the matrix consists of a glassy matrix and ferroelectric nanoclusters.Item Electric-field-induced dielectric anomalies and optical birefringence in Pb(Mg1/3Nb2/3)1-xTixO3 (x=0.10) single crystal(2006) Tu, Chi-Shun; Wang, F.-T.; Chien, R.R.; Schmidt, V. Hugo; Lim, L.-C.This work aims to study thermal stability, frequency response, and refractive indices in a (001)-cut Pb(Zn1∕3Nb2∕3)0.90Ti0.10O3 (PZNT10%) crystal before and after an electric (E)-field poling, which are important for piezoelectric and optical uses. Dielectric permittivities have been measured as functions of temperature, frequency, and poling strength. The dielectric absorption reveals a broad dipolar relaxation in the region of 260–310K in the unpoled sample. Piezoelectric resonances were observed in the poled sample and show significant changes while phase transitions are taking place. The unpoled crystal shows almost no birefringence, indicating that the structure averaged over the optically anisotropic ferroelectric domains is optically isotropic. Birefringence appears after an E-field poling and shows a “negative” uniaxial distortion. The Cauchy equations for ordinary no and extraordinary nerefractive indices were determined between 0.45 and 1.4μm. However, the phase-matching criterion for second harmonic generation was not found.Item Prior poling effect on thermal phase stability in (110)-cut Pb(Mg1/3Nb2/3)0.74Ti0.26O3 single crystal(2005) Chien, R.R.; Schmidt, V. Hugo; Tu, Chi-Shun; Wang, F.-T.Phases and domains in a (110)-cut Pb(Mg1∕3Nb2∕3)0.74Ti0.26O3 (PMNT26%) single crystal have been investigated as functions of temperature and dc electric (E) field by dielectric permittivity, polarizing microscopy, and electric polarization. The unpoled sample has a dominant rhombohedral (R) phase, which coexists with monoclinic (M) phase domains, i.e., R∕M at room temperature. With 45kV∕cm dc poling applied along [110] at room temperature, a single domain of R phase with polar orientation perpendicular to the poling field, i.e., Ṟ, was obtained. After the poling was removed, the poled sample has Ṟ/M microdomains, where the M distortion is close to the R phase. The zero-field-heating domain patterns in both unpoled and poled samples exhibit continuous polarization rotation via an intrinsic M phase in the regions of 355-375 and 365-380 K, respectively. Orthohombic and tetragonal phases were not observed in the temperature-dependent study. In general, a rhombohedral/monoclinic→monoclinic→cubic transition sequence takes place upon heating for unpoled and poled samples.Item 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.Item 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.Item Electric-field effects of dielectric and optical properties in Pb(Mg1/3Nb2/3)0.65Ti0.35O3 crystal(2005) Tu, Chi-Shun; Wang, F.-T.; Chien, R.R.; Schmidt, V. Hugo; Tuthill, G. F.Dielectric properties and domain structure have been measured as functions of temperature in a (001)-oriented Pb(Mg1∕3Nb2∕3)0.65Ti0.35O3 (PMNT35%) single crystal with and without a prior dc electric (E)-field poling. Without E-field poling, the dielectric loss exhibits a frequency-dependent maximum in the region of 120–180K, which can be described by a Vogel–Fulcher equation and fractal cluster model which implies structural irregularities within domains. With a prior poling a long-range monoclinic (tetragonal)→tetragonal (monoclinic) transition takes place near 212K upon heating. “Monoclinic (tetragonal)” represents that dominant monoclinic phase domains coexist with a small fraction of tetragonal phase domains. Optical transmission and birefringence were significantly enhanced by a prior E-field poling. The Cauchy equations for ordinary no and extraordinary nerefractive indices were determined between 0.45 and 1.4μm. However, the phase-matching criterion for second-harmonic generation was not found.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 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)].