Browsing by Author "Yeh, C.-H."

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Hypersonic and dielectric anomalies of (Pb(Zn1/3Nb2/3)O3)0.905(PbTiO3)0.095 single crystal
(1999-09-01) Tu, Chi-Shun; Chao, F.-C.; Yeh, C.-H.; Tsai, Chih-Long; Schmidt, V. Hugo
Both the longitudinal (LA) Brillouin backscattering spectra and dielectric permittivities along the [001] direction have been measured as a function of temperature for relaxor-ferroelectric single-crystal (Pb(Zn1/3Nb2/3)O3)0.905(PbTiO3)0.095 (PZN-9.5%PT). A sharp ferroelectric phase transition (which is associated with a sharp Landau-Khalatnikov-like phonon damping maximum) was observed near 460 K. As the temperature decreases, a diffuse phase transition (which is associated with a broad acoustic phonon damping maximum) was detected near 340 K. This broad damping evolution is attributed to dynamic order-parameter fluctuations. In addition, the nature of the thermal hysteresis for the dielectric permittivity confirms that these transitions (near 340 and 460 K) are diffuse first order and first order, respectively. The frequency-dependent dielectric data ɛ′′c(f,T) prove the existence of an electric dipolar relaxation process below 360 K. The activation energy, the Vogel-Fulcher temperature, and attempt frequency corresponding to this relaxation process are also calculated.
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.