Isofrequency Opalescence in Ferroelectrics

Isofrequency dependences of the spectral intensities of inelastic scattering in LiTaO₃, Pb₅Ge₃O₁₁, BaTiO₃, and KNbO₃ crystals are registered at a fixed frequency of the spectrometer close to that of the exciting radiation. Results from soft mode analysis are presented.     

Ferroelectrics in Plasma Chemistry

The qualitative considerations are presented concerning the use of plasma, generated at the surface of ferroelectric samples, for the investigation of chemical processes. The physical principles of the phenomena, its possibilities and limitations are described. Also, preliminary conclusions resulting from the investigations carried out up to the present, are drawn up.     

铁电物理的近期发展

介绍了铁电体物理学的基本概念、发展简史、近年来的主要进展以及当前的研究方向。指出铁电体物理学研究的核心是自发极化，发现历史可分为四个阶段。近年来的主要进展有四方面，即：第一性原理的计算，铁电相变的尺寸效应，铁电液晶和铁电聚合物，集成铁电体。当前的研究方向主要有两个，一是低维系统，二是调制结构。     

Orientational Relaxation in Ferroelectrics of Tetragonal Symmetry

The energy absorption caused by rotation of the spontaneous and induced polarization vectors in external longitudinal alternating-sign stress field is calculated for the barium titanate ferroelectric of tetragonal symmetry. The acoustic absorption coefficient, the internal friction, and the E effect together with their frequency and orientational dependences are derived in terms of elastic and piezoelastic constants, components of the electrostriction tensor, and rotational dissipation coefficients. The given dissipation type can dominate in ferroelectric magnets with strong coupling of their elastic, electrical, and magnetic subsystems.     

Defect-Dipole Formation in Copper-Doped PbTiO3 Ferroelectrics

The defect structure of hard copper-modified polycrystalline PbTiO3 ferroelectrics is investigated by means of electron paramagnetic resonance and hyperfine sublevel correlation spectroscopy, as well as density functional theory calculations. Special emphasis is put on the 207Pb-hyperfine couplings, which are resolved up to the third coordination sphere. The results prove that copper is incorporated at the octahedrally coordinated Ti site, acting as an acceptor. Because of charge compensation the formation of Cu impurity-oxygen vacancy pairs is energetically very favorable. The corresponding (CuTi'-VO)x defect dipole is found to be orientated along the [001] axis.     

Mathematical Modeling of the Polarization of Polycrystalline Ferroelectrics

General patterns of the polarization models of Rayleigh, Preisach, and Jiles–Atherton are found. The limiting dependence of the polarization is confirmed. A way of constructing it based on the energy criterion for domain switching for polycrystalline ferroelectrics with perovskite structure is proposed. Differential equations are constructed for determining the irreversible components of polarization and deformation, and large loops of dielectric hysteresis are calculated.     

Er-Yb Codoped Ferroelectrics for Controlling Visible Upconversion Emissions

Under a 980 nm laser pumping, quenching of green upconversion (UC) emission accompanied with enhancement of red UC emission observed was dominated by the energy back-transfer (EBT) process in Er³⁺ and Yb³⁺ co-doped PbTiO₃, BaTiO₃, and SrTiO₃ polycrystalline powders. The efficiency of the EBT process depends not only on Yb³⁺ concentration but also on level match of the doped Er³⁺ and Yb³⁺ ions caused by the crystal fields with different symmetries. Our UC emission spectra and X-ray diffraction confirm that the centrosymmetric crystal field arising from reducing tetragonality causes level match of transition of Er³⁺ and of Yb³⁺. This level match is responsible for enhancing red UC emission.     

飞秒脉冲激光在铁电体中的冲击受激拉曼散射

将冲击受激拉曼散射应用于某些铁电体中 ,在时间域内分析物质晶格振动。τωα <2π是应用冲击受激拉曼散射的必要条件。使用钛宝石激光再生放大系统作为激发源 ,在LiTaO3 晶体内获得了声子电磁激元振荡模。将同种方法用于KDP ,在其铁电体相位转换点以上 5 0K的温度范围内 ,仅发现了波矢 q =6848cm- 1 ,弛豫时间常数τ0 =1 33× 10 - 1 3 s的弛豫振动软模 ,显示出KDP铁电体相位转换的弛豫特性。     

Ferroelectrics in the para phase in a homogeneous,intense vhf field

Conclusion Investigation of the behavior of ferroelectrics in an intense variable electric field has revealed a number of significant features. The choice of models explaining the observed effects requires that the interaction between the electric field and the acoustic vibrations of the crystal lattice of the material be taken into account, demonstrates the role of static charged defects, and reveals features of charge-carrier kinetics.The main interest centers on investigations in the vhf range, which is distinguished by high information content. Here, primarily, the small wavelength of the acoustic vibrations ( l m) at frequencies of the intense excitation comparable with the film thickness and the crystallite size must be noted, together with the small duration of the vibration period, comparable with the charge-carrier relaxation time.The next problem is the creation of a model combining both the nonlinear effects and the charge-carrier kinetics determining the redistribution of the static internal field and the charge transfer. The development of such a model will have a decisive influence in improving the characteristics of ferroelectric devices.The development of microscopic models explaining the noted features of the ferroelectric properties is also very urgent. One of the interesting trends in this field is the use of the interband theory of ferroelectricity.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 59–80, August, 1981.     

Ferroelectrics with composition gradient: On the nature of hysteresis loop shift

Possible reasons of the difference in polarization characteristics of thin-film and bulk ferroelectrics with a composition gradient have been considered.     

Ferroelectrics of homogeneously deformed rare-earth garnet crystals,excited by elastic wave propagation

The effect of deformation on the electric properties in rare-earth garnet compounds is elucidated. It is shown that inhomogeneous deformation causes the emergence of electric polarization in garnet crystals on account of nonequivalent low-symmetry sites of rare-earth ions in the cubic structure of these crystals, whose symmetry of the environment has no inversion center. The polarization of a rare-earth ion subsystem in garnet crystals is studied upon the elastic wave propagation therein.

     

Phase Diagrams of Solid Solutions of Relaxor Ferroelectrics from the Dielectric Spectroscopy Data

The dielectric spectra of Pb(_1–z)Ba _z (Mg_1/3Nb_2/3) _m (Zn_1/3Nb_2/3) _y (Ni_1/3Nb_2/3) _n TixO₃ (x = 0.25–0.4, y = 0.1130–0.0842, m = 0.4844–0.1298, n = 0.1266–0.4726, z = 0–0.15) ceramics with substitution in both A and B crystallographic positions of the perovskite structure are studied. The system demonstrates a transition from the relaxor state to the normal ferroelectric state in both cases: when the concentration of lead titanate grows and the concentration of barium is reduced. On the basis of experimental results, the x–T and z–T phase diagrams are plotted. Despite different crystal chemical reasons of the relaxor state emergence in the investigated solid solutions, their diagrams demonstrate an evident similarity. We have revealed the disappearance of the temperature hysteresis at the transition to the relaxor state in both cases, which has allowed us to make an assumption of the existence of tricritical points on the corresponding diagrams.     

Phase Transitions of KIO3 Ferroelectrics in Al2O3-Based Nanoporous Matrices

Physics of the Solid State - Temperature dependences of the linear permittivity ε' and the third harmonic amplitude γ3ω of composites prepared by introducing ferroelectrics KIO3...     

Microdomain Engineering in Waveguide and Layered Structures Based on Ferroelectrics for Applications in Photonic Elements (Brief Review)

JETP Letters - Studies of ferroelectric nano- and microdomain structures formed in LiNbO3-based optical waveguides are reviewed. Nanodomain structures of a given configuration have been written in...     

1/<Emphasis Type="Italic">E</Emphasis><Superscript>2</Superscript> Law: Solution of the Unsolved Problem in the Physics of Ferroelectrics

An unusual frequency dependence of a coercive field observed in polycrystalline ferroelectric films of Pb(Zr_{1 ? x}Ti_x)O₃ solid solutions in a wide frequency range has been explained within the model of surface sources emitting thin ferroelectric domains with reversed polarization. This model makes it possible to interpret experimental data as the manifestation of the coercivity paradox in polycrystalline films and predicts the existence of the limiting frequency for switching of domains in agreement with the experiment. The proposed mechanism of polarization switching explains the observed temperature dependence of the activation field E_a ∝ T^?1/2. Furthermore, it predicts an increase in the activation energy for the nucleation of domains with an increase in the size of the source, indicating that the coercive field increases with the degradation of small