The dielectric and optical (optical transmission, small-angle light scattering, birefringence) properties of PMNT-0.2 single crystals and their variation induced by a dc electric field have been studied. The birefringence was found to increase anomalously at the transition from the rhombohedral ferroelectric to the inhomogeneous relaxor phase (the spontaneous ferroelectric transition temperature Tsp). Below Tsp, the dielectric and optical properties were observed to exhibit anomalies originating from reorientation and growth of domains in size. Unlike ferroelectric relaxors of the type of PbB′1/3B′2/3O3 and PbB′1/2B′1/2O3, in PMNT-0.2 neither induction of the ferroelectric phase by an electric field nor thermally stimulated destruction of the ferroelectric state occurs through the percolation mechanism (i.e., they are not accompanied by anomalously narrow maxima in small-angle light scattering). This is attributed to the inhomogeneous structure of the relaxor phase, as a result of which the phase transition does not take place simultaneously in various regions of the crystal. 相似文献
Ferroelectric and dielectric properties of bilayered ferroelectric thin films, SrBi4Ti4O15 grown on Bi4Ti3O12, were investigated. The thin films were annealed at 700°C under oxygen atmosphere. The bilayered thin films were prepared
on a Pt(111)/Ti/SiO2/Si substrate by a chemical solution deposition method. The dielectric constant and dielectric loss of the bilayered thin
films were 645 and 0.09, respectively, at 100 kHz. The value of remnant polarization (2Pr) measured from the ferroelectric thin film capacitors was 60.5 μC/cm2 at electric field of 200 kV/cm. The remnant polarization was reduced by 22% of the initial value after 1010 switching cycles. The results showed that the ferroelectric and dielectric properties of the SrBi4Ti4O15 on Bi4Ti3O12 ferroelectric thin films were better than those of the SrBi4Ti4O15 grown on a Pt-coated Si substrate suggesting that the improved properties may be due to the different nucleation and growth
kinetics of SrBi4Ti4O15 on the c-axis-oriented Bi4Ti3O12 layer or on the Pt-coated Si substrate. 相似文献
The ferroelectric domain structures of periodically poled KTiOPO4 and two‐dimensional short range ordered poled LiNbO3 crystals are determined non‐invasively by interferometric measurements of the electro‐optically induced phase retardation. Owing to the sign reversal of the electro‐optical coefficients upon domain inversion, a π phase shift is observed for the inverted domains. The microscopic setup provides diffraction‐limited spatial resolution allowing us to reveal the nonlinear and electro‐optical modulation patterns in ferroelectric crystals in a non‐destructive manner and to determine the poling period, duty cycle and short‐range order as well as detect local defects in the domain structure. Conversely, knowing the ferroelectric domain structure, one can use electro‐optical microscopy so as to infer the distribution of the electric field therein.
The phonon spectrum of cubic cadmium metastannate and parameters of the crystal structure of its distorted phases were calculated
from first principles within the density functional theory. It is shown that the phonon spectrum and the energy spectrum of
the distorted phases in α-CdSnO3 resemble surprisingly the corresponding characteristics of CdTiO3. The ground state of α-CdSnO3 is the ferroelectric Pbn21 phase, the energy gain from the phase transition to this phase from the nonpolar phase Pbnm is ∼30 meV, and the spontaneous polarization is 0.25 C/m2. The analysis of the eigenvector of the ferroelectric mode in α-CdSnO3 and the partial densities of states indicates that the ferroelectric instability in this crystal, which does not contain
transition d-element atoms, is associated with the formation of a covalent bonding between Cd and O atoms. 相似文献
The dielectric, optical, and electro-optical properties of transparent ferroelectric ceramics 75PbMg1/3Nb2/3O3-25PbTiO3 (75PMN-25PT) with different La concentrations (2, 3, and 4 at %) have been studied. It has been shown that all the samples
under study undergo a diffuse phase transition, and the degree of diffuseness increases with an increase in the La concentration.
The temperature dependences of the optical transmission in different regimes of applying an electric field and the quadratic
electro-optical effect have been investigated. It has been found that, at room temperature, the maximum electro-optical effect
is observed in the ceramics with a La concentration of 3 at %. This is explained by the fact that the measurement temperature
is close to the Vogel-Fulcher temperature at which the minimum electric field is required to induce ferroelectric states from
the relaxor phase. 相似文献
The results of studying the velocity of hypersonic longitudinal acoustic phonons over a wide temperature range under an applied constant electric field in the PbMg1/3Nb2/3O3 (PMN) relaxor ferroelectric are reported. An analysis of the experimental data on the basis of the existing E-T phase diagrams shows the necessity of a substantial change in the current concepts. Two radically different states—with the reversible and irreversible behavior of velocity—have been observed experimentally in the induced ferroelectric phase. A modified E-T phase diagram of the PMN crystal is suggested. 相似文献
Here we present a simple model formulated in the spirit of Landau theory in order to qualitatively describe magnetoelectric
multiferroics. The system consists of two coupled single-component order parameters P and M which represent ferroelectric and ferromagnetic phases, respectively.
We show that the magnetoelectric
coupling strongly renormalizes the original magnetic transition temperature, TM
?\rightarrow
TRM (with TRM ≫ TM), as well as generates an additional anomaly in ferroelectric subsystem at TRM.
Under the influence of both magnetic and electric fields the concept of Arrot plot is reproduced by the Arrot planes.
We compare obtained results with available experimental data for the BiMnO3 which
undergoes ferroelectric transition below 700 K (Tf)
and ferromagnetic transition at 100 K (TRM).
The results are in good overall agreement with experimental data for the ferroelectromagnetic BiMnO3. We also estimate the contribution of Gaussian fluctuations of both order parameters, that lead to corrections to the mean-field
specific heat.
Those corrections are still insufficient even though other quantities agree quite well with experiment.
We calculate the temperature dependence of the coherence length for both types of order as well. 相似文献
The dynamic Born charges and the frequency spectra of lattice oscillations in the crystals of ordered and disordered PbSc1/2Ta1/2O3 (PST) and PbSc1/2Nb1/2O3 (PSN) solid solutions have been calculated within the framework of the generalized Gordon-Kim model with allowance for the dipole and quadrupole polarizabilities. The phonon spectra of both compounds contain ferroelectric soft modes. The influence of various interactions on the magnitude of dynamic charges and ferroelectric instability in PSN and PST solid solutions has been studied and it is shown that both these charges and the ferroelectric instability are determined by the competition between long-range dipole-dipole interactions and short-range dipole-charge interactions, the determining role played by the interaction of Nb (Ta) cations and oxygen anions in the Nb-O (Ta-O) bond direction. 相似文献
The processes of polarization evolution in single crystals of the PbMg1/3Nb2/3O3 model ferroelectric relaxor in a sinusoidal electric field are investigated at temperatures near and above the temperature Td0 of destruction of the induced ferroelectric state upon heating in zero electric field. The polarization switching current loops are measured in the ac electric field applied along the 〈111〉 and 〈110〉 pseudocubic directions. The electroluminescence intensity loops are obtained under the combined action of ac and dc electric fields applied along the 〈100〉 direction. In a certain temperature range above Td0 and the freezing temperature Tf in lead magnesium niobate, there are electric current anomalies, that correspond to the dynamic formation and subsequent destruction of the ferroelectric macroregions throughout each half-cycle of the ac electric field. The measurements of electroluminescence hysteresis loops demonstrate that the observed depolarization delay (related to the ac electric field amplitude) increases with an increase in the dc electric field and decreases as the ac field amplitude increases. The nature of the observed phenomena is discussed. 相似文献
Layered-perovskite ferroelectric Bi2.85La0.15TiNbO9 (LBTN) optical waveguiding thin films were grown on fused silica substrates by pulsed laser deposition (PLD). X-ray diffraction
(XRD) revealed that the film is highly (00l) textured. We observed sharp and distinct transverse electric (TE) and transverse magnetic (TM) multimodes and measured the
refractive indices of LBTN thin films at 632.8 nm. The ordinary and extraordinary refractive indices were calculated to be
nTE=2.358 and nTM=2.464, respectively. The film homogeneity and the film-substrate interface were analyzed using an improved version of the
inverse Wentzel–Kramer–Brillouin (iWKB) method. The refractive index of the film remains constant at n0 within the waveguiding layer. The average transmittance of the film is 70% in the wavelength range of 400–1400 nm and the
optical waveguiding properties were evaluated by the optical prism coupling method. Our results showed that the LBTN films
are very good electro-optical active material. 相似文献
The temperature dependences of the permittivity, birefringence, optical transmittance, and small-angle light scattering and their variations with time are studied for single crystals of the Pb0.94Ba0.06Sc0.5Nb0.5O3 relaxor (PBSN-6) in the heterophase region of coexistence of different phases. It is shown that an electric field induces a phase transition to the ferroelectric state, which manifests itself within some time (delay time τ) after application of the electric field to the crystal. The observed dependence of the temperature of this transition on the heating rate of the sample and the changes in the birefringence and small-angle light scattering intensity with time confirm the kinetic character of the induced transition. Temperature dependences of the delay time τ for different electric fields are constructed. It is revealed that, at low temperatures, the delay time τ decreases with increasing temperature. This agrees with the behavior of τ in classical relaxors. At the Vogel-Fulcher temperature, however, one observes that dτ/dT reverses sign and τ increasing as the temperature continues to increase. This anomalous behavior of τ in the heterophase region is accounted for by the coexistence of the cubic relaxor and rhombohedral macrodomain phases. 相似文献
Epitaxial SrTiO3 thin films were deposited on single crystalline Rh substrates by pulsed laser deposition. The tetragonally stained structure of the SrTiO3 thin films with a c/a ratio of 1.04 was confirmed by x-ray diffraction experiments. The SrTiO3 thin films exhibited good ferroelectric properties with a high remanent polarization (2Pr) of 8 μC/cm2 and a canonical ferroelectric piezoresponse hysteresis loop at room temperature. We estimated a high activation electric field of about 6.4 MV/cm for domain wall creeping. This activation electric field is higher than that of typical ferroelectric materials such as PbTiO3. 相似文献
We report on the ac dielectric permittivity (ε) and the electric conductivity (σω), as function of the temperature 300?K?T400?K and frequency 0.5–100?kHz for polycrystalline samples of hydrogen-bonded ferroelectric ammonium iodate, NH4IO3. The main feature of our measured parameters is that, the compound undergoes a ferroelectric phase transition of an improper character, at (368?±?1)K from a high temperature paraelectric phase I (Pm21b) to a low temperature ferroelectric phase II (Pc21n). The electric conduction seems to be protonic. The frequency dependent conductivity has a linear response following the universal power law (σ(ω)?=?A(T)ωs(T)). The temperature dependence of the frequency exponent s suggests the existence of two types of conduction mechanisms. 相似文献