Anomalous properties of crystals with ferroelectric phase transition induced by off-center ions

It is given the theoretical study of some properties of strongly polarizable dielectric crystals in which off-center impurity ions induce ferroelectric phase transition. The spontaneous polarization, transition temperature, soft mode frequency, dielectric susceptibility, ultrasonic attenuation, nuclear spin-lattice relaxation are analyzed. The theory explains observed in K_1?xLi_xTaO₃ saturation of remanent polarization with off-center Li⁺ concentration increasing, close to $\text{x}$ dependence of phase transition temperature, the anisotropy of ultrasonic attenuation, the absence of anomalies of Li nuclear spin-lattice relaxation rate near T_c.     

Mechanisms of off-center ion behavior in oxygen-octahedral perovskite-type ferroelectrics

A mechanism of the off-center impurity-ion behavior induced by the quadratic Jahn-Teller effect on polar distortions and (or) joint action of the local electrostriction and linear Jahn-Teller effect on nonpolar distortions is proposed. The off-center behavior of Ni⁵⁺ and Fe⁴⁺ ions in the incipient ferroelectric KTaO₃ is substantiated. It is shown that, in the limit of neglecting the correlation between off-center Li⁺ ions, their displacements from KNbO₃ lattice sites decrease, whereas, under the conditions of strong correlation, a critical increase in their displacements from lattice sites occurs with approaching the Curie point.     

Dielectric and ferroelectric properties of NBT-BT systems

ABSTRACT

The (1-x)Na_0.5Bi_0.5TiO₃- xBaTiO₃ ceramics (x = 0.1, 0.135 and 0.17) were fabricated by a conventional solid phase sintering process. The bulk density of the obtained samples exceeded 95% of the theoretical relative density as determined by Archimedes method. Dielectric and ferroelectric measurements of these ceramics were performed. Measurements of the ferroelectric properties show that, above the depolarization temperature T_d, the shape of the hysteresis loops approaches that of linear dielectrics. The dielectric study results correlate with the hysteresis loops measurements. The relaxor-like behavior of the investigated materials was revealed.     

Li and Nb codoping in dielectric properties and phase transitions of KTaO3: Reentrant dipolar glass and long-range dipole ordering

Abstract

The highly polarizable perovskite-type oxide, KTaO₃ doped simultaneously with Li⁺ and Nb⁵⁺ (K_1?xLi_xTa_1?yNb_yO₃, KLTN), reveals unexpected properties and ordering effects. Studies of the dielectric permittivity ?'(T, f) (10—300K, 100Hz-1 MHz) for x = 0.0014 and y = 0.024 show collective dipolar ordering effects with a transition from paraelectric into a mixed phase (coexisting dipole-glass-like and long-range ordered ferroelectric phases) taking place near 39 K. At 15 K another phase transition into a reentrant dipolar glass-like state is observed. Such a sequence of transitions and the existence of a reentrant glass state are unknown for electrical dipolar systems.     

Electromechanical-induced antiferroelectricben ferroelectric phase transition in PbLa(Zr,Sn,Ti)O3 ceramic

Antiferroelectric—ferroelectric (AFE—FE) phase transition in ceramic Pb_0.97La_0.02(Zr_0.75Sn_0.136Ti_0.114)O₃ (PLZST) was studied by dielectric spectroscopy as functions of frequency (10²—10⁵ Hz) and pressure (0—500 MPa) under a DC electric field. The hydrostatic pressure-dependent remnant polarization and dielectric constant were measured. The results show that remnant polarization of the metastable rhombohedral ferroelectric PLZST poled ceramic decreases sharply and depoles completely at phase transition under hydrostatic pressure. The dielectric constant undergoes an abrupt jump twice during a load and unload cycle under an electric field. The two abrupt jumps correspond to two phase transitions, FE—AFE and AFE—FE.     

Magnetic and ferroelectric properties of exchange-frustrated multiferroics (Ni1 ? xTx)3V2O8 (T = Co, Mn, Zn)

The effect of the substitution of Co²⁺, Mn²⁺, and Zn²⁺ ions for Ni²⁺ ions on the magnetic, dielectric, and ferroelectric properties of vanadate single crystals (Ni_{1 − x} T _x )₃V₂O₈ has been analyzed. It has been found that the low-level (x ≤ 0.1) substitution of both magnetic and nonmagnetic ions stabilizes the ferroelectric state with a cycloidal magnetic structure. The existence region of this state is expanded to low temperatures down to 3 K for Zn²⁺ and below 1.8 K for Co²⁺ and Mn²⁺ owing to the suppression of a low-temperature weak ferromagnetic phase. At the same time, the ferroelectric phase disappears completely at large concentrations of Co and Mn. The effect of magnetic fields on the magnetic and ferroelectric states has been analyzed. It has been shown that the magnetic field along the c axis suppresses the ferroelectric state, whereas the magnetization along the antiferromagnetism axis (a axis) induces the reentrant phase transition from a paraelectric weak ferromagnetic structure to a ferroelectric structure. The corresponding H-T phase diagrams have been drawn.     

Fluorescence of rare-earth ions in dirty displacive ferroelectrics

The phase transition of ferroelectric Sr_1?xBa_xNb₂O₆ was studied by measuring the fluorescence emitted from the rare-earth ions doped as a probe. The fluorescence spectral width and the wavelength showed singular behavior around the transition temperature. The samples possess a diffuse transition with characteristic optical properties near the inflection point of the temperature-dependence curve of the spontaneous polarization.     

Dielectric nonlinearity of crystalline Li2−x NaxGe4O9 (x≈0.23)

The dielectric nonlinearity of ferroelectric Li_2−x Na_xGe₄O₉ (x≈0.23) crystals is measured in the neighborhood of the phase transition temperatures. The magnitude of the nonlinear coefficient β is estimated from the shift in T _c and the reduction in ɛ _max under the influence of E ₌, from the dielectric nonlinearity in the paraphase, and from the temperature dependence of P _s in crystalline Li_2−x Na_xGe₄O₉ (x≈0.23). The resulting values of β are 1.87, 1.26, 2.17, and 1.17×10⁻⁹ (CGSE cm²)⁻², respectively. The mechanism for the phase transition in crystalline Li_2−x Na_xGe₄O₉ (x≈0.23) is discussed. Fiz. Tverd. Tela (St. Petersburg) 41, 1070–1072 (June 1999)     

Phase coexistence in proton glass

Abstract

Proton glasses are crystals of composition M_1?x(NW₄)_xW₂A0₄, where M = K,Rb,Cs, W = H,D, A = P, As. For x = 0 there is a ferroelectric (FE) transition, while for x-1 there is an antiferroelectric (AFE) transition. In both cases, the transition is from a paraelectric (PE) state of tetragonal structure with dynamically disordered hydrogen bonds to an ordered state of orthorhombic structure. For an intermediate x range there is no transition, but the hydrogen rearrangements slow down, and eventually display nonergodic behavior characteristic of glasses. We and others have shown from spontaneous polarization, dielectric permittivity, nuclear magnetic resonance, and neutron diffraction experiments that for smaller x there is coexistence of ferroelectric and paraelectric phases, and for larger × there is coexistence of antiferroelectric and paraelectric phases. We present a method for analytically describing this coexistence, and the degree to which this coexistence is spatial and/or temporal. We discuss also the experimental determination of these coexistence parameters.     

Self-localized carrier states in disordered ferroelectrics

A theory of self-localized states of free carriers near polarization fluctuations (fluctuons) in disordered ferroelectrics is developed. Calculations are carried out for the model disordered ferroelectric K_{1− x} Li_xTaO₃ (x≪0.05). The basic characteristics of the fluctuon — the energy and radius of the fluctuon state — are calculated as functions of the impurity dipole concentration and temperature. The theory predicts the appearence of stable fluctuon states in both the mixed ferroelectric-dipole-glass phase (a dipole glass is the electric analog of a spin glass) and the dipole-glass state of disordered ferroelectrics. The possible role of fluctuons in kinetic phenomena such as conductivity in these substances is discussed. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 5, 425–429 (10 March 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Nd掺杂对Bi4Ti3O12铁电薄膜的微结构和铁电性能的影响

利用溶胶-凝胶法在Pt/Ti/SiO₂/Si(100)衬底上制备了Nd掺杂Bi₄Ti₃O₁₂(Bi_4-xNd_xTi₃O₁₂, x=0.00,0.30,0.45,0.75,0.85,1.00,1.50)铁电薄膜样品.研究了Nd掺杂对Bi₄Ti₃O₁₂薄膜的微结构和铁电性能的影响.研究结果表明:Nd掺杂未改变Bi₄Ti₃O₁₂薄膜的基本晶体结构.在掺杂量x<0.45时,Nd³⁺只取代类钙钛矿层中的A位Bi³⁺.当x=0.45时,样品剩余极化强度达最大值,在270kV·cm^-1的电场下为32.7μC·cm^-2.掺杂量进一步增加时,结构无序度开始明显增大,Nd³⁺开始进入(Bi₂O₂)²⁺层,削弱其绝缘层和空间电荷库的作用,导致材料剩余极化逐渐下降.当掺杂量x达到1.50时,掺杂离子最终破坏(Bi₂O₂)²⁺层的结构,材料发生铁电-顺电相变.     

Crystallographic and optical properties of Li1−xTa1−xEu2xO3 solid solutions

Abstract

The effects of europium substitution on crystalline solubility, structural changes and optical properties of Li_1?xTa_1?xEu_2xO₃ solid solutions are reported. The solid solutions exist over a very limited range of europium concentrations (x ≤ 0.02). They were characterized by X-ray powder diffraction and density measurements. The liquid nitrogen fluorescence and excitation spectra of Eu³⁺ in the solid solutions were measured in the frequency range 12,200–45,450 cm^?1. The emission mainly arises from the ⁵ D ₀ level to Stark components of the five lowest ⁷ F _j (j = 0, 1, 2, 3, 4) states. It was inferred from the analyses of the optical and density data that the Eu³⁺ ions may lie on both Li and Ta sites, but not on the intrinsic vacant lattice sites.     

Evolution of the ferroelectric phase in ?001?-oriented (100 ? x )PbMg1/3Nb2/3O3- x PbTiO3 single crystals

The effect of a dc electric field on the nucleation and evolution of the phase with long-range order in a cubic nonpolar matrix in 〈001〉-oriented (100 − x)PbMg_1/3Nb_2/3O₃-xPbTiO₃ single-crystal relaxors as the content of PbTiO₃ is gradually increased (6 ≤ x ≤ 20, where x is the PbTiO₃ content given in molecular percent) is investigated. The optical properties of these solid solutions are studied in different modes of application of an electric field. It is shown that an applied electric field with a strength above a threshold value induces a first-order ferroelectric phase transition with a temperature hysteresis occurring between measurements performed under cooling and heating of the crystal in the electric field. As the PbTiO₃ content or electric field strength increases, the hysteresis becomes less pronounced and the first-order phase transition is suppressed. At x ∼ 20, the induced transition resembles a second-order rather than first-order transformation. It is assumed that, for compositions with x > 10 in electric fields higher than 4 kV/cm, the formation of the rhombohedral phase is accompanied by the appearance of another (possibly, monoclinic) phase associated with the rotation of the polarization vector from the [111] direction of the rhombohedral phase to the [001] direction of the tetragonal phase. Original Russian Text ? L.S. Kamzina, E.V. Snetkova, I.P. Raevskiĭ, A.S. Emel’yanov, Jiayue Xu, Weidong Xiang, 2007, published in Fizika Tverdogo Tela, 2007, Vol. 49, No. 4, pp. 725–730.     

Experimental indication of macroscopic polarization parallel to the tilt plane in free-standing films of ferroelectric liquid crystals 8SI* and DOBAMBC

Optical reflectivity and x-ray studies have been conducted on free-standing films and bulk samples of ferroelectric liquid crystals near the smectic-A-smectic-C ^* transition. A tilt plane rotation with respect to the direction of an applied electric field is found in the ferroelectric films above the bulk transition temperature. Whereas the macroscopic polarization is perpendicular to the tilt plane at low temperature, it is parallel to the tilt plane at elevated temperature. The temperature dependence of the average tilt angle is measured. Zh. éksp. Teor. Fiz. 116, 1329–1334 (October 1999) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Ferroelectric properties of SrTiO3-PbTiO3 solid solutions

Dielectric properties of ceramic samples of Sr_1−x Pb_xTiO₃ solid solutions for x varying from 0 to 0.3 have been studied. The ferroelectric phase transition in this system has been established to persist down to x=0.005. Within the x values of 0.002 to 0.05, the ferroelectric transition temperature is shown to follow the relation T _c=A(x−x _c)^1/2, with A=440 K and x _c=0.002. Fiz. Tverd. Tela (St. Petersburg) 39, 714–717 (April 1997)     

Simultaneous measurement of X‐ray diffraction and ferroelectric polarization data as a function of applied electric field and frequency

The characteristics of a new ferroelectric measurement system at the European Synchrotron Radiation Facility are presented. The electric‐field‐induced phase transitions of Pb(Mg_1/3Nb_2/3)O₃–xPbTiO₃ are determined viain situ measurements of electric polarization within the synchrotron diffraction beamline. Real‐time data collection methods on single‐crystal samples are employed as a function of frequency to determine the microstructural origin of piezoelectric effects within these materials, probing the dynamic ferroelectric response.     

Observation of electric polarization in Gd<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript>x</Subscript>MnO<Subscript>3</Subscript> (<Emphasis Type="Italic">x</Emphasis> = 0.5, 0.6, 0.7) single crystals

In Gd_1?xSr_xMnO₃ (x = 0.5, 0.6, 0.7) single crystals, a change in electric polarization (ΔP ～ 100 μK/m²) is found to accompany the suppression of the charge-ordered spin-glass state and the transition to the ferromagnetic conducting phase (H_cr ～ 100 kOe at 4.5 K). The transition is also characterized by jumps in magnetization and magnetostriction. The sign of the induced polarization depends on the polarity of the electric field in which the sample was preliminarily cooled. This dependence testifies to the presence of spontaneous electric polarization in the system. The effect is maximal at x = 0.5 and decreases by more than an order of magnitude as x increases to 0.7. The phenomenon observed in the experiment may be associated with the new noncentrosymmetric structures with an electric dipole moment that were recently predicted for manganites (x ～ 0.5) [Nature Materials 3, 853 (2004)]. These structures exhibit charge-orbital ordering such that e _g electrons are not localized by one of the manganese ions but distributed between neighboring ions, thus forming an ordered dimer structure.     

Time relaxation of permittivity in [(CH3)2NH2]3CuCl5 crystal under external electric field

Continuation of our previous studies connected with dielectric properties of tris-dimethylammoniumpentachlorocuprate crystal [(CH₃)₂NH₂]₃CuCl₅ crystal under the influence of electric field are presented in this article. We studied the time dependence of the permittivity under the influence of electric field at constant temperatures above T _c. In experiment, slow but significant decrease of permittivity was observed, which can be described with two main relaxation processes. The observed dielectric behavior can be related to the coexistence of phases and slow transition to ferroelectric one through long-time metastable states connected with the presence of incommensurate phase in the studied crystal. The coexistence of phases and slow transition was confirmed from the appearance of induced polarization under external electric field, measured as depolarization current.     

Ferroelectric phase stabilization, phase transformations and?thermal properties in (1? x )PbZrO3– x Pb(Co1/3Nb2/3)O3 solid solution

The solid solution between the antiferroelectric PbZrO₃ (PZ) and relaxor ferroelectric Pb(Co_1/3Nb_2/3)O₃ (PCoN) was synthesized by the columbite method. The phase structure and thermal properties of (1−x)PZ–xPCoN, where x=0.0–0.3, were investigated. With these data, the ferroelectric phase diagram between PZ and PCoN has been established. The crystal structure data obtained from XRD indicates that the solid solution PZ–PCoN, where x=0.0–0.3, successively transforms from orthorhombic to rhombohedral symmetry with an increase in PCoN concentration. The AFE→FE phase transition was found in the compositions of 0.0≤x≤0.10. The AFE→FE phase transition shift to lower temperatures with higher compositions of x. The width of the temperature range of FE phase was increased with increasing amount of PCoN. It is apparent that the replacement of the Zr⁴⁺ ion by (Co_1/3Nb_2/3)⁴⁺ ions would decrease the driving force for antiparallel shift of Pb²⁺ ions, because they interrupt the translational symmetry. This interruption caused the appearance of a rhombohedral ferroelectric phase when the amount of PCoN was more than 10 mol%.     

An origin of infinite range dipole-dipole correlations in soft matrices with off-center impurities: K 1−x Li x Ta 1−y Nb y O 3 and other systems

A model of cooperative behaviour for K 1 m x Li x Ta 1 m y Nb y O 3 (KLTN) and for other disordered systems like ferroelectric relaxors is considered from the point of view of contribution of infinite-range dipole-dipole interactions. It is shown that a local piezoeffect for off-center impurities in crystals with rather high electrostriction is responsible as origin of a infinite-range electric dipole-dipole interaction via elastic fields as well as for a co-existence of ferroelectric and glass-like states with reentrant glass effect.