Anomalous light diffusion in ferroelectrics having a diffuse phase transition

It has been shown by using the statistical approach that the angular dependence of intensity I(θ) in multiple small-angle light scattering can be described by Lévy’s universal distribution functions. The fundamental property of the stability of these distributions permits one to extract information on the characteristics of fractal media as complete as it is possible in the simple single-scattering case. In particular, an analysis of the polarization characteristics of I(θ) in disordered PST reveals that the surface fractals observed in these crystals are of the heterophase rather than domain origin. Fiz. Tverd. Tela (St. Petersburg) 40, 1537–1541 (August 1998)     

Kinetics of nucleation of thermodynamically ordered ferroelectric phases in PbMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript>–<Emphasis Type="Italic">x</Emphasis>PbTiO<Subscript>3</Subscript> crystals with different compositions

The kinetics of electric field-induced nucleation of ordered ferroelectric phases from a mixed glassy relaxor state has been studied in a number of single-crystal (1–x)PbMg_1/3Nb_2/3O₃–xPbTiO₃ (PMN–xPT) solid solutions (x = 29, 33, 35%) lying in a morphotropic phase region. It is shown that the formation of these phases and fast establishment of a macroscopic polarization are preceded by some delay time, depending on the electric field strength and temperature. It is found that the monoclinic phase is thermodynamically stable at room temperature in all the compounds in the time (~3000 s) and electric field (~1 kV/cm) ranges under study, whereas the monoclinic phase of the compound with x = 35% transforms, at temperatures near the temperature of the morphotropic phase transition after insignificant time interval of ~100 s, to another stable ferroelectric tetragonal phase.     

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.     

Analysis of the conditions favoring the onset of long-range order in disordered relaxors of different types

The possibility of realizing a stable relaxor behavior in PbSc_1/2Nb_1/2O₃ (PSN) compounds and the conditions favoring the formation of a phase with long-range order in PbZn_1/3Nb_2/3O₃ (PZN) are studied using optical methods. It is found that the replacement of only 6% of Pb ions with Ba ions (PBSN-6) freezes the relaxor state in PSN compounds, while adding even 7% of PbTiO₃ to the PZN relaxor (PZN-7PT) leads to the formation of a phase with long-range order and a phase transition occurring at T _maxε through the percolation mechanism. Common features in the formation and destruction of the long-range order phase in relaxors of different types are revealed. The differences associated with the presence of spontaneously polarized ferroelectric regions in the cubic nonpolar matrix of PSN-type compounds are determined.     

Time Dependences of Dielectric and Acoustic Properties in PbFe0.5Nb0.5O3 and PbFe0.5Nb0.5O3–7PbTiO3 Single Crystals

Physics of the Solid State - The time changes of permittivity, damping and velocity of sound are studied for PbFe0.5Nb0.5O3 and PbFe0.5Nb0.5O3–7PbTiO3 single crystals in the electric fields...     

Hysteresis phenomena in the course of polarization evolution in a sinusoidal electric field in lead magnesium niobate crystals

The processes of polarization evolution in single crystals of the PbMg_1/3Nb_2/3O₃ model ferroelectric relaxor in a sinusoidal electric field are investigated at temperatures near and above the temperature T _d 0 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 T _d 0 and the freezing temperature T _f 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.     

Intermediate phases in [111]- and [001]-oriented PbMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript>–29PbTiO<Subscript>3</Subscript> single crystals

Phase transformations in [111]- and [001]-oriented PbMg_1/3Nb_2/3O₃–29PbTiO₃ single crystals have been studied using dielectric and optical measurements before and after applying an electric field. It is shown that the subsequence of phase transitions rhombohedral (R)—tetragonal (T)—cubic (C) phases is observed in nonpolarized samples of both orientations as temperature increases. In the [111]-oriented crystal, an additional intermediate monoclinic phase (it is possible, M _a ) is induced after preliminary polarization at room temperature and the R–M _a –T–C phase transitions are observed on heating. In the [001]-oriented crystal, after its polarization, the monoclinic phase forms instead of the rhombohedral phase even at room temperature and the M _a –T–C transitions occur on heating. The results are discussed from the point of view of the existence polar nanoregions with different local symmetries in a glasslike matrix.     

Polarization Kinetics in Transparent Pb(Mg1/3Nb2/3)O3–23Pb(Zr0.53Ti0.47)O3 Ceramic

Physics of the Solid State - The polarization kinetics in a transparent Pb(Mg1/3Nb2/3)O3–23Pb(Zr0.53Ti0.47)O3 ferroceramic is investigated in the electric fields of 0 &lt; E &lt; 6...     

Effect of La Concentration on the Kinetics of the Induced Phase Transition in PbMg1/3Nb2/3O3–25PbTiO3 Transparent Ceramics

Physics of the Solid State - The effect of La concentration on the kinetic character of the induced phase transition in PbMg1/3Nb2/3O3–25PbTiO3 ferroceramics is studied. Below the...     

Influence of the electric field on structural transformations and phase boundary for PMg1/3Nb2/3O3-xPbTiO3 single crystals

The influence of different regimes of application of a dc electric field (0 < E < 4 kV/cm) on structural phase transformations and behavior of the phase boundary in [001]-oriented single crystals PMg_1/3Nb_2/3O₃-xPbTiO₃ (PMN-xPT) with compositions near the morphotropic phase boundary (x = 28 and 32%) and far from it (x = 13%) has been investigated. The studies have been performed using optical methods, namely, optical transmittance and small-angle light scattering. It has been revealed that the number, symmetry, and stability of field-induced phases depend on the regime of electric field application. During cooling of the PMN-28PT crystals from the cubic phase in the field (FC regime), the tetragonal phase is induced already in weak fields of ∼0.5 kV/cm, whereas even a field of 3 kV/cm is insufficient for inducing this phase by applying the field in the ferroelectric phase. In the PMN-32PT crystal (which has a composition closer to the morphotropic phase boundary as compared to that of the PMN-28PT crystal) in the FC regime and when the field is applied in the ferroelectric phase, the tetragonal phase is induced already in weak electric fields, even though this phase in the latter case appears to be unstable. The E-T phase diagrams have been constructed for different regimes of field application. The possible factors responsible for the observed differences have been discussed.