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Phase transformations of (110)-cut Pb(Mg1/3Nb2/3)0.70Ti0.30O3 single crystal before and after an electric (E)-field poling have been investigated by means of dielectric permittivity, polarization current, hysteresis loop, and in situ x-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, the crystal underwent an R-O(R)-T-C phase sequence with significant responses in polarization current. O(R) represents that the minor R phase coexists in the orthorhombic matrix. The dielectric permittivities with and without a prior poling were found to follow the Curie–Weiss equation, [variant_greek_epsilon]′=C/(T-T0), above the Burns temperature 505 K with the same constants C=1.43×105 K and T0=462 K. [ABSTRACT FROM AUTHOR]

Dielectric permittivity, electric polarization, and domain structure have been carried out as a function of temperature in 0.5 mol % WO3-doped Pb(Mg1/3Nb2/3)0.65Ti0.35O3 (PMNT35%) single crystal. Two first-order-type temperature-dependent phase transitions, monoclinic (rhombohedral)→monoclinic→cubic, were observed near 310 K (290 K) and 440 K (435 K) upon heating (cooling), respectively. “Monoclinic (rhombohedral)” represents that dominant monoclinic domains coexist with a small fraction of rhombohedral domains. Reorientations of monoclinic domains are mainly responsible for the low-temperature steplike dielectric anomaly. This study shows that WO3 dopant can enhance monoclinic domains whose dynamics play an important role in temperature-dependent structural transitions. [ABSTRACT FROM AUTHOR]

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 260–310 K 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 ne refractive indices were determined between 0.45 and 1.4 μm. However, the phase-matching criterion for second harmonic generation was not found. [ABSTRACT FROM AUTHOR]

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 120–180 K, 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 212 K 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 ne refractive indices were determined between 0.45 and 1.4 μm. However, the phase-matching criterion for second-harmonic generation was not found. [ABSTRACT FROM AUTHOR]

Dielectric permittivity and loss of \ BiFeO3 (BFO) and 5 mol% lanthanum-substituted BFO [(\ Bi0.95{\ {La}}0.05){\ {FeO}}3 or BFO-5% La] ceramics have been carried out as functions of temperature and frequency. A frequency-dependent and broad dielectric shoulder and maximum were observed in BFO and BFO-5% La near 600–700 K. These dielectric responses are likely due to the magnetoelectric coupling while the antiferromagnetic–paramagnetic transition takes place near the Néel temperature. As an approximation, a barrier model with intrinsic barriers B (in temperature unit) every lattice constant a and extrinsic barriers B +\Delta every distance d is introduced to describe the low-frequency upturn in dielectric loss in the high-temperature region. Good qualitative fits are obtained for BFO and BFO-5% La. This work suggests that 5 mol% La substitution can enhance dielectric response and considerably reduce electric conductivity. [ABSTRACT FROM AUTHOR]

The article discusses a study on dielectric, domain and optical phenomena induced by electric fields in high-strain Pb(In½Nb½)1-xTixO3 (x=0.30) single crystal. The study measured dielectric permittivity, domain structure and electric polarization in the crystal before and after an electric-field poling. It found that long-range percolations were broken near 390 K as temperature increases. It showed that the dielectric permittivity follow the Curie-Weiss behavior.

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. [ABSTRACT FROM AUTHOR]

This work investigates dielectric and photovoltaic behaviors in Pb(Mg1/3Nb2/3)0.64Ti0.36O3 single crystal doped with 0.5 mol % 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=406 nm) illumination for the poled samples can be expressed by an exponential equation. Optical transmission reveals that the cutoff wavelength is near 400 nm and indicates a minimum electronic energy gap of ∼3.0 eV. [ABSTRACT FROM AUTHOR]