Electromechanical Hysteresis Research Articles

New electrostrictive ceramics for sonar projector applications.

Relaxor ferroelectric ceramics, in particular lead magnesium niobate–lead titanate (Pb3MgNb2O9–PbTiO3) compositions, have potential for hydroacoustic transducer applications. In an unbiased state, the strain-versus-electric field relationship is nonlinear (largely quadratic) with respect to the electric polarization. By applying a large dc bias voltage simultaneously with a small ac signal, acoustic signals whose amplitudes are linear with respect to the ac signal are produced. The strains produced are of similar magnitude to those of lead zirconate–titanate ceramics. Several specific compositions have been examined in order to optimize the material by reducing the dielectric and electromechanical hysteresis, the temperature dependence of dielectric properties, and the dielectric aging and the results are discussed. The possibility of being able to switch the polarization of the material off with the biasing field makes the further development of these materials intriguing. [This work supported by ONR.]

Complex investigations of electrostrictive PMN-ceramics

Abstract We investigated the small and high signal electromechanical behaviour, the temperature and frequency dependence of pure and mixed PMN-ceramics with special respect to the temperature dependence of electrostriction and the width of temperature region without electromechanical hysteresis. We explain the large electrostriction by two different mechamisms and present an extraordinary big electrostrictive effect in PLZT-ceramics.

Thermodynamical formulation for coupled electromechanical hysteresis effects—IV. Combined electromechanical loading

In this work we present some possible scenarii of hysteresis and loading paths which can be envisaged through electromechanical couplings in a ferroelectric circular cylinder subjected to torsion and a longitudinal electric field. This has been carried out on the basis of a previously devised thermodynamical model for coupled electromechanical hysteresis effects in ferroelectric materials. Discarding the work hardening and micro-effects related to ferroelectric wall motions we introduce only an internal electric variable. The proposed combined electromechanical loading paths could be realized experimentally.

Thermodynamical formulation for coupled electromechanical hysteresis effects—II. Poling of ceramics

In this work, we use the model developed in Part I [1] to deduce a consistent set of thermodynamical relations for the description of the poling of ceramics. With the appropriate identifications, these relations can be considered as a thermodynamical basis for Chen's theory which did not rely on thermodynamics. Time-dependent effects (akin to viscosity) and rate-independent effects (like in the mechanical behaviour known as “plasticity”) are investigated. An integrodifferential equation for the density of aligned dipoles is obtained. Some simple experimental methods are suggested for the determination of the different material coefficients introduced in the modeling.

Thermodynamical formulation for coupled electromechanical hysteresis effects—I. Basic equations

In this work we present a thermodynamical phenomenological formulation of a theory capable of displaying electromechanical hysteresis effects in continous media, which should apply to ferroelectric ceramics. This is built within the scheme of the thermodynamical theory of internal variables. This theory produces both plastic and electric-hysteresis effects in the form of “plasticity”, i.e. rate-independent, evolution equations for the plastic strain, the residual electric polarization and both mechanical and electric “hardenings”. This paper develops in detail the electric hardening effects through the residual polarization vector and an internal variable representing an electric polarization. An electric version of Drucker's inequality of plasticity has been derived. Several examples of loading functions are studied including the influence of piezoelectric and electrostrictive couplings. In particular, the purely electric loading function has been studied in greater detail and the first polarization curve either based on experimental data or theoretically displayed is discussed. In all the paper provides all ingredients for a future discussion of more specific cases.

Temperature-dependence of electromechanical coupling and strain in barium titanate hafnate transducer

The electromechanical coupling factor and ferroelectric hysteresis loops were investigated at different temperatures for BaTio.ssHfo.tsO3 transducer. Maxirhum polarization and strain were obtained near the transition of the crystal structure. This correlated with increases in the ease and extent of ferroelectric domain boundary motion. The change in the crystal structure varied the unit cell volume, leading to higher strain. BaTiO3 and Pb(Ti, Zr)O 3 and their compositions containing different concentrations of doping ions have strong piezoelectric effects. The earliest investigations of the piezoelectric properties in these compositions [1-7] showed the coupling factor to be highest near the tetragonal-rhombohedral phase boundary. Compositions rich in PbTiO3 were not successfully poled, but a significant piezoelectric effect existed throughout the rhombohedral range. It is believed that the proximity to such a phase boundary between ferroelectric phases favours strong piezoelectrics in a ceramic, because of the increased ease of reorientation during poling. Subsequent work has yielded samples with much stronger piezoelectric coupling [5]. This resulted from a better ceramic quality and an improved poling technique. Instead of a maximum planar coupling factor of 0.4, values over 0.6 at room temperature have been achieved, both in these unmodified solid solutions and in others with various degrees of additional compositional modification. These compositions, as a class, are more useful than BaTiO3 compositions. In the present work, the electromechanical coupling factor and the ferroelectric hysteresis loops were investigated, with particular attention to tme behaviour of the system BaTio.85Hfo.1503 near the rhombohedral-cubic phase boundary. Large values of the coupling kp and spontaneous polarization p and strain have been reported near this phase boundary from cheap and unvolatile materials during the sintering process.

Temperature dependence of electromechanical properties and strain in barium titanate hafnate transducers

The electromechanical coupling factor and ferroelectric hysteresis loops were investigated at different temperatures for BaTi0.85Hf0.15O3 transducer. Maximum polarization and strain were obtained near the transition of the crystal structure. This correlated with increases in the ease and extent of ferroelectric domain boundary motion. The change in the crystal structure varied the unit cell volume, leading to higher strain.

Electromechanical hysteresis measurements: A new tool for investigation of the properties of plastics

AbstractThe charge‐strain hysteresis curve can be measured by simple apparatus. While fundamental interpretation of the effect may be complex, the use of the curves for practical purposes such as investigation of fatigue, quality control, differentiation between materials or methods of preparation or surface characteristics, is simple. The effect shows indication of being related to the chemical nature of the material, its composition and structure, and particularly the phase or quasi‐phase structure. Chargestrain hysteresis curves have been measured. These are quite reproducible if the samples from which specimens are prepared are uniform. The shape of the hysteresis curve is affected by (1) amplitude of strain, (2) rate of straining, including constant strains, (3) the functional dependence of strain upon time, (4) repeated cycling, (5) incorporation of fillers, (6) incorporation of reinforcing fibers, (7) the mechanical properties of the plastic, (8) detailed composition of the polymers, and (9) temperature. Seven general types of hysteresis curve are observed. The general features of the curve, and the hysteresis area are sensitive methods for detecting slight changes for composition. This method of sample differentiation was illustrated with examples showing the magnitude and sensitivity of the effect. When a sample was held at a given strain, the charge decreased; this suggests that both resistivity, and the initial stages of mechanical plastic flow may be observed indirectly through this phenomenon. Continuously repeated cycling shows a change in charging‐strain response related apparently to the initial stages of flexural fatigue. A regular decrease of hysteresis area is observed with repeated cycling, with the area decrease depending upon the plastic composition. The rate of decline of the area with repeated cycling is a second method for differentiating between materials, particularly when differences are obscured in other methods of testing.