L. Eric Cross

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...

Relaxorferroelectrics: An overview

Abstract The paper will trace the evolution of understanding related to the modification of sharp ferroelectric phase transition behavior that occurs in composition systems which exhibit diffuse and relaxor ferroelectric properties. The focus will be primarily upon the perovskite structure families where cations of different valence occupying similar crystallographic sites in the structure appear to play an important role. Limited ordering in the Pb(B1B2)O3 systems will be discussed and possible mechanisms for self limiting to nanometer scales in some systems explored. New studies of the break up of the simple ferroelectric behavior in lanthanum modified lead zirconate titanate (PLZT) and in lead titanate (PLT) systems will be discussed and the relevance to the general problem of relaxor behavior examined. Evidence for enhanced polarization fluctuations and super paraelectric behavior at high temperatures will be discussed and random field and spin glass models for the lower temperature state considered. ...

Enhanced piezoelectric property of barium titanate single crystals with engineered domain configurations

Piezoelectric properties of barium titanate single crystals were investigated at room temperature as a function of crystallographic orientation. When a unipolar electric field was applied along [001], its strain vs electric-field curve showed a large hysteresis, and finally barium titanate crystal became to single-domain state with piezoelectric constant d33 of 125 pC/N over 20 kV/cm. On the other hand, electric-field exposure below 6 kV/cm along [111] resulted in a high d33 of 203 pC/N and a hysteresis-free strain vs electric-field behavior, which suggested the formation of an engineered domain configuration in a tetragonal barium titanate crystal. Moreover, when an electric field over 6 kV/cm was applied along [111], two discontinuous changes were observed in its strain vs electric-field curve. In situ domain observation and Raman measurement under an electric field suggested an electric-field-induced phase transition from tetragonal to monoclinic at around 10 kV/cm, and that from monoclinic to rhombohedral at around 30 kV/cm. Moreover, in a monoclinic barium titanate crystal, electric-field exposure along [111] resulted in the formation of another new engineered domain configuration with d33 of 295 pC/N.

Domains in Ferroic Crystals and Thin Films

A Preview of Concepts and Phenomena.- Fundamentals of Ferroic Domain Structures.- Ferroic Materials.- Methods for Observation of Domains.- Static Domain Patterns.- Domain Walls at Rest.- Switching Properties: Basic Methods and Characteristics.- Switching Phenomena and Small-Signal Response.- Ferroelectric Thin Films.

Flexoelectric polarization of barium strontium titanate in the paraelectric state

The strain-gradient-induced polarization (flexoelectric effect) was investigated in Ba0.67Sr0.33TiO3 (BST) ceramic at temperatures above the 21 °C Curie point. At 23 °C the flexoelectric coefficient μ12 was more than one order of magnitude greater than the highest value measured in lead magnesium niobate ceramic. Over the temperature range of linear Curie–Weiss behavior, the coefficient μ12 was roughly proportional to the dielectric permittivity; however, the constant of proportionality was higher than predicted for simple ionic solids. The unexpected behavior in the BST ceramic suggests the need for a broader database of flexoelectric coefficients.

Stress induced shift of the Curie point in epitaxial PbTiO3 thin films

A 50 °C shift in Curie temperature has been observed for c‐axis oriented PbTiO3 thin films using x‐ray diffraction. An analysis of the electrostrictive strain based on the Devonshire thermodynamic formalism showed that the shift in the Curie point for these films can be plausibly explained by an effective two‐dimensional compressive stress of ≊400 MPa. The single‐domain, single‐crystal dielectric susceptibility (η33) and piezoelectric coefficient (d33) were calculated and found to be relatively unaffected, at room temperature, by a compressive stress of this magnitude.

Electric field dependence of piezoelectric properties for rhombohedral 0.955Pb(Zn1/3Nb2/3)O3– 0.045PbTiO3 single crystals

The electric field dependence of the piezoelectric properties of rhombohedral 0.955Pb(Zn1/3Nb2/3)O3–0.045PbTiO3 crystals were investigated as a function of orientation with respect to the prototypic (cubic) axes. For 〈111〉 oriented fields, depolarization and subsequent domain reorientation resulted in an apparent maximum in the piezoelectric coefficients occurring at ∼5 kV/cm, followed by nonhysteretic dij saturation, indicating a single domain state under bias. By extrapolation, single domain values for the piezoelectric coefficients d33 and d31 were determined to be 125 and −35 pC/N, respectively. The hydrostatic piezoelectric coefficient dh for single domain crystals was calculated to be ∼55 pC/N, coincident with the experimentally determined values under hydrostatic pressure. For 〈001〉 oriented fields, piezoelectric coefficients d33〈001〉 and d31〈001〉 as high as 2250 and −1000 pC/N were determined, respectively. Although a high value of dh〈001〉 (∼250 pC/N) was expected, the experimentally determined va...

Flexoelectricity of barium titanate

Flexoelectricity was investigated as a function of temperature in paraelectric and ferroelectric phases of barium titanate ceramic. The flexoelectric coefficient μ12 was measured dynamically at small level of strain gradients. μ12 is around 5μC∕m in orthorhombic phase, rises to about 10μC∕m at room temperature, and peaks at ∼50μC∕m near tetragonal-cubic phase transition point. The coupling effect between mechanical strain gradient and electric polarization is found to be nonlinearly enhanced by high dielectric permittivity and domain contribution in barium titanate. In inhomogeneously strained ferroelectrics, mechanical gradient field may impact electric polarization in a way analogous to electric field.

Nonlinear piezoelectric behavior of ceramic bending mode actuators under strong electric fields

The nonlinear electromechanical behavior of cantilevered piezoelectric ceramic bimorph, unimorph, and reduced and internally biased oxide wafer actuators is studied in a wide electric field and frequency range. It is found that under quasistatic condition, linear relationships between actuator tip displacement-electric field, and blocking force-electric field are only valid under weak field driving. With increasing the driving field, electromechanical nonlinearity begins to contribute significantly to the actuator performance because of ferroelectric hysteresis behavior associated with piezoelectric lead zirconate titanate (PZT)-type ceramic materials. The bending resonance frequencies of all these actuators vary with the magnitude of the electric field. The decrease of resonance frequency with electric field is explained by the increase of elastic compliance of PZT ceramic due to elastic nonlinearity. Mechanical quality factors of the actuators also depend on the magnitude of electric field strength. No ...

Ferroelectric Ceramics: Tailoring Properties for Specific Applications

Ferroelectric oxide ceramics are used in a very broad range of functional ceramics and form the materials base for the majority of electronic applications. These electronic applications account for more than 60% of the total high technology ceramics market worldwide (High Technology Ceramic News, 1990). It is the purpose of this tutorial paper to examine the range of physical properties which make the ferroelectrics attractive for electronic applications and the techniques which can be used to modify, control and optimize these families of properties.