S. J. Jang

Freezing of the polarization fluctuations in lead magnesium niobate relaxors

The dielectric relaxation of a solid solution of 10‐mol % lead titanate in lead magnesium niobate is found to be similar to the magnetic relaxation in spin‐glass systems.1–3 Based on this analogy, it is proposed that the relaxor ferroelectric is a polar‐glassy system which has thermally activated polarization fluctuations above a static freezing temperature. An activation energy and freezing temperature of 0.0407 eV and 291.5 K, respectively, were found by analyzing the frequency dependence of the temperature of the dielectric maximum using the Vogel–Fulcher relationship.4,5 It has also been shown that a macroscopic polarization is sustained on heating up to this freezing temperature. A coupling between nanometer scale clusters is believed to control the kinetics of the fluctuations and the development of a frustration as the system freezes into states of local equilibrium. The possibility of an orientational freezing associated with the ferroelastic nature of the nanosized polar regions in the rhombohedr...

Dielectric and pyroelectric properties in the Pb(Mg1/3Nb2/3)O3-PbTiO3 system

Abstract Dielectric and pyroelectric properties of relaxor ferroelectric in the (1-x) Pb(Mg1/3Nb2/3)O3-xPbTiO3 solid solution series have been investigated. The dielectric constant (K) and loss of poled and unpoled ceramic samples were determined. The pyroelectric coefficient and the spontaneous polarization were measured by the static Byer-Roundy method as a function of temperature and for various compositions in the binary system PMN-PT. An important contribution to the dielectric and pyroelectric behavior for the solid solutions compositions close to the morphotropic phase boundary (x ∼ 0.4) between pseudocubic and tetragonal regions existing in the grains of the ceramic were observed. Anomalous dielectric and pyroelectric behaviors occurred for compositions x = 0.275 ∼ 0.35 mole% PT in the vicinity of morphotropic phase boundary.

Thermodynamic theory of PbTiO3

A phenomenological thermodynamic theory of PbTiO3 was developed using a modified Devonshire form of the elastic Gibbs free energy. The spontaneous strain as a function of temperature was determined from pure sol‐gel derived PbTiO3 powder and used with selected data from the literature to determine the coefficients of the energy function. The theoretical prediction of the phase stability, spontaneous polarization and strains, and dielectric and piezoelectric properties agree well with experimental data. This theory provides a way of predicting the intrinsic single domain dielectric and piezoelectric properties of PbTiO3, which have not been completely determined from experimental measurements.

Electrostrictive effect in lead magnesium niobate single crystals

Transverse and longitudinal elastic strain have been measured for electric fields applied along the 〈100〉 direction in single crystals of lead magnesium niobate [Pb(Mg1/3Nb2/3)03], using a bonded strain gauge technique. A quadratic electrostrictive relation holds between induced elastic strain and electric polarization for temperatures near the low‐frequency dielectric maximum. The electrostriction coefficients are almost temperature independent with values Q11=2.50×10−2 m4/C2 and Q12=−0.96×10−2 m4/C2. To check the direct measurements, the hydrostatic Q coefficient was determined independently by measuring the pressure dependence of the dielectric permittivity. The value Qh =0.60×10−2 m4/C2 obtained is in good agreement with that calculated from the direct measurements.

Thermodynamic theory of the lead zirconate-titanate solid solution system, part I: Phenomenology

Abstract Compositions within the lead zirconate-titanate (PZT) solid solution system have been extensively used in polycrystalline ceramic form in a wide range of piezoelectric transducer applications. However, the growth of good quality PZT single crystals for compositions across the entire phase diagram has not been accomplished. Due to the lack of single-crystal data, an understanding of the properties of polycrystalline PZT has been limited. If the single domain (intrinsic) properties of PZT could be determined, then the extrinsic contributions (e.g. domain wall and defect motions) to the polycrystalline properties could be separated from the intrinsic contributions. The purpose of this research has been to develop a thermodynamic phenomenological theory to model the phase transitions and single-domain properties of the PZT system. This paper is the first of a series of five papers describing the thermodynamic theory of PZT that has been developed for the entire solid solution system. In this paper th...

Large electrostrictive effects in relaxor ferroelectrics

Lead magnesium niobate and other relaxor ferroelectrics are promising transducer materials for use as active elements in adaptive optic systems and similar applications. These ceramics are dominantly in the paraelectric phase, and dimension control is obtained through the high intrinsic quadratic electrostrictive effect. Since stable ferroelectric domain structures do not occur, the problems of dimensional creep and non-reproducibility (aging and de-aging effects) of the conventional poled piezoelectric ceramic are largely eliminated. Suitably chosen compositions in the Pb3MgNb2O9-PbTiO3 family give electrostriction strains ten times larger than those of conventional BaTiO3-based ceramics. Low expansion coefficients are an added advantage for thermal stability.

Thermodynamic theory of the lead zirconate-titanate solid solution system, part III: Curie constant and sixth-order polarization interaction dielectric stiffness coefficients

Abstract Vaiues of the Curie constant (C) and sixth-order polarization interaction dielectric stiffness coefficients (α112 and α123) are needed for the development of a thermodynamic theory for the entire lead zirconate-titanate (PZT) solid solution system. Low-temperature dielectric data measured on pure homogeneous polycrystalline PZT samples were used to determine values of these coefficients at several compositions across the phase diagram. Equations were then fitted to these data to determine the compositional dependence of the coefficients. The Curie constant was found to form a peak in the middle of the phase diagram at the PZT 50/50 composition.

Domain wall excitations and their contributions to the weak‐signal response of doped lead zirconate titanate ceramics

The ac field dependence of the polarization and strain responses of three different compositions of doped lead zirconate titanate ceramics were measured for samples in both the poled and the depoled states. The results indicate that a reversible domain wall excitation exists which contributes to the weak‐signal response of these materials. Irreversible domain wall motion can be excited within the frequency range measured by applying a field above a threshold field, which is much smaller than the coercive field. Therefore, the weak‐signal linear dielectric, piezoelectric, and elastic coefficients of these materials may not provide a suitable description of their behavior when the external applied field exceeds this threshold field. All the observed phenomena can be explained by thermally activated domain wall fluctuations and nucleations.

Thermodynamic theory of the lead zirconate-titanate solid solution system, part V: Theoretical calculations

Abstract In this final paper of a sequence of five papers presenting details of a thermodynamic phenomenology for the whole PbZrO3 : PbTiO3 solid solution family, the constants derived in the earlier papers are used to calculate the temperature and composition dependence of the Elastic Gibbs Free Energy ΔG 1 at zero stress, the spontaneous electric polarization and spontaneous tilt of the oxygen octahedra in a single domain, the anisotropic weak field dielectric permittivity and the piezoelectric constants for compositions all across the phase diagram. These data can be used to determine the intrinsic component of the behavior of any pure lead zirconate : lead titanate in any part of the phase field and at any temperature, and thus can form a first step in the separation of the experimentally observed properties into their intrinsic (single domain) component and their extrinsic domain and defect related responses. The function proposed is certainly not the final word for PZT, and will clearly be subjected...

Morphotropic phase boundary in Pb (Mg13Nb23) O3-PbTiO3 system

Abstract Dielectric and pyroelectric properties in the solid solution (1 −x) Pb (Mg 1 3 Nb 1 3 ) O 3 : xPbTiO 3 across the morphotropic phase boundary compositions, x = 0.275–0.4, are studied as a function of temperature. The studies revealed that the true morphotropic boundary is in the vicinity of x≈ 0.3 and it has a small curvature.