Browsing by Author "Luo, H."

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Dielectric and relaxation behaviors of (PbMg1/3Nb2/3O3)0.67(PbTiO3)0.33 single crystal
(2006) Tu, Chi-Shun; Schmidt, V. Hugo; Luo, H.; Chao, F.-C.
Dielectric permittivity along the [111] direction has been measured as a function of temperature for a relaxor ferroelectric single crystal (PbMg1/3Nb2/3O3)0.67(PbTiO3)0.33 (PMN-33%PT). A sharp ferroelectric phase transition was observed near 425 K and 429 K for cooling and heating processes, respectively. As temperature decreases, a diffuse phase transition (which begins near 330 K upon cooling) was detected. In addition, the nature of the thermal hysteresis for the dielectric permittivity confirms that these transitions (near 330 and 425 K upon cooling) are diffuse first-order and first-order, respectively. The frequency-dependent dielectric data ∊′111 (ƒ, T) prove the existence of an electric dipolar relaxation process between 350 and 400 K. The activation energy, the Vogel-Fulcher temperature and attempt frequency corresponding to this relaxation process are also calculated.
Dielectric, hypersonic, and domain anomalies of (PbMg1/3Nb2/3O3)1-x(PbTiO3)x single crystals
(2001) Tu, Chi-Shun; Tsai, Chih-Long; Schmidt, V. Hugo; Luo, H.; Yin, Z.
Dielectricpermittivities,Brillouinbackscattering spectra, polarization-electric field hysteresis loops, and domain structures have been measured as a function of temperature in relaxor-based ferroelectricsingle crystals(PbMg1/3Nb2/3O3)1−x(PbTiO3)x(PMN-xPT)(PbMg1/3Nb2/3O3)1−x(PbTiO3)x(PMN-xPT) for x=0.24x=0.24 and 0.34. For PMN-24%PT, a diffuse phase transition which is associated with a broad frequency-dependent dielectric maximum was observed near 380 K. As the temperature increases, the PMN-24%PT crystal gradually develops cubic regions and is fully converted into the cubic state near 375 K. An extra dielectric anomaly appears at 370 K, possibly due to the percolating polar cluster induced by an external electric field. PMN-34%PT exhibits a nearly normal ferroelectric phase transition near 445 K from the tetragonal to the cubic phase. In addition, a weak diffuse phase transition observed near 280 K may result from partial conversion of rhombohedral phase to tetragonal phase. The dielectric thermal hysteresis confirms that the transitions near 280 and 445 K are diffuse first order and first order, respectively. The dielectricpermittivities of PMN-24%PT and PMN-34%PT obey the relation, ε′m/ε′(f,T)=1+[T−Tm(f )]γ/2δ2γ,εm′/ε′(f,T)=1+[T−Tm(f )]γ/2δγ2, above the temperature of permittivity maximum Tm.
Elastic, piezoelectric, and dielectric properties of 0.58Pb(Mg1/3Nb2/3)O3-0.42PbTiO3 single crystal
(2004) Cao, H.; Schmidt, V. Hugo; Zhang, Rui; Cao, W.; Luo, H.
The elastic,piezoelectric, and dielectric constants of 0.58Pb(Mg1/3Nb2/3)O3-0.42PbTiO30.58Pb(Mg1/3Nb2/3)O3-0.42PbTiO3 (PMN-42%PT) were determined experimentally using combined resonance and ultrasonic methods. At room temperature the PMN-42%PT single crystal has tetragonal symmetry. The measured piezoelectric constantd33d33 is ∼260×10−12 C/N.∼260×10−12 C/N. The electromechanical coefficients k15,k15, k31,k31, k33,k33, and ktkt are 0.80, 0.39, 0.78, and 0.62, respectively. From the measured material constants the orientational dependence of phase velocities and electromechanical coupling coefficients was calculated. The results showed the tetragonal crystal exhibits isotropy in the X-YX-Y plane and k15,k15, k33,k33, and ktkt reach their maxima in [001].
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.
Field-induced intermediate orthorhombic phase in (110)-cut Pb(Mg1/3Nb2/3)0.70Ti0.30O3 single crystal
(2008) Tu, Chi-Shun; Schmidt, V. Hugo; Chien, R.R.; Tsai, S H; Lee, S.-C.; Luo, H.
Intermediate phases in rhombohedral Pb(Mg1/3Nb2/3)1-xTixO3 crystal
(2008) Tu, Chi-Shun; Chuang, H.-T.; Lee, S.-C.; Chien, R.R.; Schmidt, V. Hugo; Luo, H.
Phase transformations of (111)-cut Pb(Mg1∕3Nb2∕3)1−xTixO3 (x=0.30) single crystals before and after an electric (E)–field poling have been investigated by means of dielectricpermittivity, hysteresis loop, polarization current, and in situx-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 dielectricpermittivities with and without a prior poling were found to follow the Curie–Weiss equation, ε′=C/(T−T0), above the Burns temperature 505K with the same constants C=1.9×105 K and T0=460K.
Light scattering and dielectric measurements in (PbMg1/3Nb2/3O3)0.67(PbTiO3)0.33 single crystal
(2000) Schmidt, V. Hugo; Tu, Chi-Shun; Yeh, C.-H.; Luo, H.; Chao, F.-C.
The longitudinal Brillouin back-scattering spectra, dielectric permittivities and polarization-electric field (P-E) hysteresis loops along the [111] direction have been measured as a function of temperature for a relaxor ferroelectric single crystal (PbMg1/3Nb2/3O3)0.67(PbTiO3)0.33 (PMN-33%PT). A sharp ferroelectric phase transition, which is associated with a minimum in phonon frequency and an abrupt change in polarization, was observed near 425 K. As temperature decreases, a diffuse phase transition which is associated with a broad frequency-dependent dielectric spectrum and a gradual evolution in polarization, was detected near 350 K. In addition, the nature of the thermal hysteresis for the dielectric permittivity confirms that these transitions (near 350 and 425 K) are diffuse first-order and first-order, respectively. The field-cooled-zero-field-heated dielectric permittivities show that the dc bias field induces a long-range ferroelectric phase transition at 357 K and imply the phase coexistence of a short-range electric ordering and a long-range electric ordering in the region of ∼330–380 K.
Phase coexistence and Mn-doping effect in lead-free ferroelectric (Na1/2Bi1/2)TiO3 crystals
(2010) Tu, Chi-Shun; Huang, S.-H.; Ku, C. -S.; Lee, H.-Y.; Chien, R.R.; Schmidt, V. Hugo; Luo, H.
Phase transformations of (001)-cut (Na1/2Bi1/2)TiO3 (NBT) and 1 at. % Mn-doped NBT (Mn-NBT) crystals have been investigated by means of dielectric permittivity, conventional x-ray diffraction (XRD), and high-resolution synchrotron XRD and reciprocal space mapping. An R−R+T−T−C transition sequence was observed in NBT and Mn-NBT upon zero-field heating. R, T, and C are rhombohedral, tetragonal, and cubic phases, respectively. R+T represents that the ferroelastic T phase coexists with the ferroelectric R phase. The Mn dopant can enhance dielectric response and reduce the dielectric loss in the high-temperature region due to the increased degree of ordering.
Piezoelectric response and origin in (001) Pb(Mg1/3Nb2/3)0.70Ti0.30O3 crystal
(2008) Tu, Chi-Shun; Hsieh, C.-M.; Schmidt, V. Hugo; Chien, R.R.; Luo, H.
Converse and direct piezoelectric coefficients (dC33 and dD33) of (001)-cut Pb(Mg1/3Nb2/3)0.70Ti0.30O3 (PMN-30%PT) single crystals have been investigated as a function of poling electric (E) field. E-field-dependent domain structures were observed by using a polarizing microscope. Both dC33 and dD33 exhibit a rapid increase at E=1–2 kV/cm and reach maxima at E=2.5–4 kV/cm. This study suggests that polarization rotation from rhombohedral to monoclinic MA phases plays an important role while the high piezoelectric response builds up. Overpoling phenomenon evidenced by a sudden reduction in piezoelectric coefficient with increasing field is very sensitive to Ti content.
Rapid piezoelectric response and origin in (001) Pb (In1/2Nb1/2)0.70Ti0.30O3 crystal
(2009) Tu, Chi-Shun; Chien, R.R.; Lee, S.-C.; Schmidt, V. Hugo; Luo, H.
Normal piezoelectric coefficient d33, domain structure, and x-ray diffraction of a (001)-cut Pb(In1/2Nb1/2)0.70Ti0.30O3 (PIN-30%PT) single crystal have been investigated as a function of poling electric (E) field. E-field-dependent domain structures were observed by using a polarizing microscope. Piezoelectric coefficient d33 exhibits a rapid increase at E=1–3 kV/cm and reaches a maximum of about 1200 pC/N near E=6 kV/cm. Structurald spacing and domain structure results suggest that polarization rotation from rhombohedral to monoclinic MA phases causes the high piezoelectric response. Overpoling phenomenon associated with a sudden reduction of d33 with increasing field was not evidenced.