Glassy Polarization Research Articles

EFFECT OF ADDITION OF BT ON RELAXOR BEHAVIOR OF PIN-PT CERAMICS

ABSTRACT Ferroelectric ceramics with chemical formula (1-x)Pb(In0.5Nb0.5)O3-(x)PbTiO3 and (1-x)Pb(In0.5Nb0.5)O3-(x)PbTiO3 with 20%mol of BT (x = 0.0, 0.1, 0.2 and 0.3) were prepared via the wolframite method. The relaxor behavior was analyzed from the dielectric properties and thermal expansion measurements. The dielectric properties were measured at frequencies between 100 Hz and 100 kHz whereas the thermal expansion was measured in the temperature range between −145°C and 500°C. It is found that the addition of BT effects the relaxor behavior of PIN-PT system. The broad and diffused dielectric constant maxima and essentially no change in Burns temperature were measured and thus suggesting the glassy polarization and relaxor behavior in the PIN-PT-BT compositions.

A-site cation ordering and the glassy polarization behavior of lanthanum-modified lead zirconate titanate

The microstructure and dielectric behavior of lanthanum-modified lead zirconate titanate with 9 at.% lanthanum and a Zr/Ti ratio of 65/35 (PLZT 9/65/35) were investigated. By analyzing the frequency dependence of the temperature of the dielectric maximum (Tm) using the Volgel-Fulcher relationship, an activation energy and freezing temperature of 0.0393 ev and 347.4 K respectively, were obtained, showing that the polarization behavior of the sample bears resemblance to spin and dipolar glasses. Both selected-area diffraction (SAD) and high-resolution electron microscopy (HREM) reveal that {h+1/2, k+1/2, 0}-type superlattice exists in the sample. The lattice images of the ordered and the disordered regions were shown directly by HREM. The size of the ordered domains is from 10-20 nm. An ordered model with body-centered cubic superstructure on A-site cations was proposed. Based on the A-site cations ordering, the dielectric polarization behavior in different temperature range was discussed.

Glassy polarization behavior of relaxor ferroelectrics.

The polarization behavior of La-modified lead zirconate titanate relaxors has been investigated for various electrical and thermal histories. The field-cooled and zero-field-cooled behaviors were both studied. The magnitude of both polarizations were found to be equal above a critical temperature. A macroscopic polarization developed, when the zero-field-cooled state was warmed with a bias applied. The temperature of the maximum charging current decreased with increasing bias field. This decrease was modeled using the deAlmeida-Thouless relationship [J. deAlmeida and D. Thouless, J. Phys. A 11, 983 (1978)], which predicted an average moment size freezing of approximately 3\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}27}$ C m. A glassy polarization mechanism was subsequently proposed with correlations between superparaelectric moments leading to the development of effective nonergodicity in a frozen state. Arguments are presented that this freezing process is dispersive due to a distribution of correlation strengths. The time dependence of the polarization was also investigated.

Study of the glassy polarization phase in the tungsten bronze family by measurements of strain, optical indices, and polarization

Abstract There has been considerable discussion of crystalline ferroelectrics with a glassy polarization phase. There are materials in which evidences for regions of local, randomly oriented polarization far above the transition temperature Tc, up to a temperature Td, have been found1.

Ferroelectrics with a glassy polarization phase

Abstract In this paper we discuss some of the measurements and properties of materials that are crystalline ferroelectrics with a glassy polarization phase. We review measurements of the temperature dependence of the optical index of refraction, n(T), which were first used to observe these properties. Then we discuss a model of these polarization effects in terms of a local, randomly oriented polarization (Pr) that may occur hundreds of degrees above Tc. This local polarization is allowed by the strong breakdown of the translational symmetry that occurs in these systems. We also show how the temperature dependence of the strain, x(T), complements the n(T) results. Lastly, we discuss some recent x-ray and EXAFS measurements and how they are in agreement with the model, and the connection between these high temperature effects and the low-temperature glass-like excitations that are found in these systems.

Properties of Tetragonal PLZT with Reference to its Diffuse Phase Transition

Measurements were made of the dielectric, elastic, electrostrictive, piezoelectric and linear thermal expansion constants together with an X-ray analysis of the hot-pressed ceramics of PLZT X/55/45, X being varied from 0 to 15. Here, a new model is introduced regarding the structure of the intermediate state between the paraelectric and the ferroelectric states, the so-called “slim-loop ferroelectric state.” It is assumed that this state is composed of polar microdomains embedded within a non-polar paraelectric matrix and whose orientations change with time. On the basis of this model, the temperature dependence of the dielectric constant and the free energy are calculated with appropriate approximations. It is also shown that this model can explain the so-called “glassy polarization” which extends far above the Curie temperature.

Soft phonons in a ferroelectric polarization glass system

Index of refraction, n(T), and Raman measurements are reported on a new crystalline ferroelectric systems that exhibits a glassy polarization phase. The crystal is Pb(Ti 1− x Sn x )O 3, which hs the simple perovskite crystal structure. From n(T) we obtain a phase transition (at a temperature T c = 430±3 C) and an upper dipole temperature (T d ≈ 500C). The Raman measurements reveal the presence of soft phonon modes and a central peak between T c and T d. These data represent the first dynamic results from such systems. T d is quantitatively understood in terms of the phase transition temperature of the end member (i.e., x = 0. Further, we give a qualitative explanation of a microscopic mechanism for the phase transition in these glassy ferroelectric systems in terms of the localized dipole interaction model. Using this model, other aspects of ferroelectric glasses are discussed.

Low-temperature thermal properties of ferroelectrics.

Through measurements of the low-temperature thermal conductivity and specific heat, we show that two classes of ferroelectrics can be distinguished. One class exhibits behavior typical of crystalline solids and the other displays behavior identical to that seen in structural glasses. We correlate these observations with measurements of the dielectric constant and optic index of refraction in the vicinity of the ferroelectric transition at ${T}_{c}$. Near ${T}_{c}$, those ferroelectrics with crystal-like thermal properties at low temperature exhibit normal behavior (i.e., a sharp ferroelectric transition) while those with glasslike thermal properties display a diffuse phase transition and a glassy polarization phase. The similarity to the elastic dipole glass (KBr${)}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$(KCN${)}_{\mathrm{x}}$ is discussed.

Crystalline Ferroelectrics with a Glassy Polarization Phase

We have studied several different ferroelectric crystal systems where the long range translational symmetry is strongly broken. From measurements of the temperature dependence of the optic index of refraction, n(T), we find that far above the ferroelectric transition temperature, Tc, there is a temperature Td where local polarization occurs. For systems such as PLZT, i.e., (Pb1-3x/2Lax)(ZryTi1-y)O3, Td is several hundred degrees above Tc and independent of La-concentration. In this system we can account for Td quantitatively (in terms of Tc of PZT, i.e., zero La concentration). The model emphasizes local polarization effects from clusters of a few unit cells.

Glassy polarization behavior inK2Sr4(NbO3)10-type ferroelectrics

We extend our previous measurements of the temperature dependence of the optic indices of refraction, $n(T)$, of two crystals of the ${\mathrm{K}}_{2}$${\mathrm{Sr}}_{4}$${(\mathrm{N}\mathrm{b}{\mathrm{O}}_{3})}_{10}$ type with different amounts of disorder. These materials are axial ferroelectrics with the tetragonal tungsten-bronze crystal structure. As in other ferroelectrics where the translational symmetry is strongly broken, a glassy polarization ${P}_{d}$ is observed far above the ferroelectric transition temperature ${T}_{c}$. However, in these noncubic materials, angular averaging of $n(T)$ need not be done, and so ${P}_{d}$ is obtained rather directly. Below ${T}_{c}$ it is in good agreement with the reversible, spontaneous polarization.

Glassy polarization behavior in ferroelectric compounds [formula omitted] and [formula omitted

We report measurements of the temperature dependence of the optic index of refraction, n(T), at several wave lengths in two ferroelectric compounds that have the simple perovskite ABO 3 structure. The compounds are Pb(Mg 1 3 Nb 2 3 ) O 3 and Pb(Zn 1 3 Nb 2 3 ) O 3 where the B-site ions are disordered. Deviations from the high temperature linear n(T) can be observed starting at a temperature T d (far above the ferroelectric phase transition temperature T c). We assume a model in which these deviations arise from very local randomly oriented polarization (i.e. glassy polarization), P d. Then, using the quadratic electrooptic effect and the known coefficients, we determine P d and compare it to the normally observed ferroelectric reversible spontaneous polarization P r. Also, from infrared reflectivity data, we show that these materials are microscopically homogeneous. We believe that our model of the phase transition contains the basic physics describing ferroelectrics with diffuse phase transitions.

The observation of glassy polarization behavior in crystalline ferroelectric materials

We summarize some of our recent measurements of the temperature dependence of the optic index of refraction, n(T), in several different classes of ferroelectrics. The common thread between these different materials is that in all of them the translational symmetry is strongly broken. Far above the usual ferroelectric transition temperature Tc up to a temperature Td, we show that the crystals possess a local, randomly oriented, nonreversible polarization. Using a simple model for this behavior, we can account for it qualitatively and in some systems quantitively understand Td. We believe this model contains the basic physical understanding of ferroelectrics that have a diffusive phase transition.

Crystalline ferroelectrics with glassy polarization behavior

We report measurements of the optic index of refraction as a function of temperature, $n (T)$, in the crystalline ferroelectrics having the simple perovskite ($\mathrm{AB}{\mathrm{O}}_{3}$) structure. We show that these crystals possess a local, randomly oriented, nonreversible polarization below a temperature ${T}_{d}$ several hundred degrees above the ferroelectric phase-transition temperature ${T}_{c}$. Using a simple model, we account for this behavior and understand quantitatively the values of ${T}_{d}$. This model, we believe, contains the basic physical understanding of ferroelectrics with a diffuse phase transition.