Transparent single crystals of the perovskite Pb(Zn-1/3,Nb-2/3)O-3-PbTiO3 (PZN-PT) were grown from different lead fluxes in sealed platinum crucibles. A temperature gradient furnace was used (temperature gradient on crucible: 30-50 degreesC). Optimization of growth temperature range and cooling rates was carried out in fluxes of PbO, Pb3O4 with and without an addition of B2O3. The growth nature range was typically 1150 degreesC --> 930 degreesC (on crucible top) with cooling rates of 0.8 - 1 degreesC/h for the Pb3O4 flux. In these conditions, the best PZN-PT transparent single crystal was 4x4x2.5mm large and it showed a cubic habitus. The problem of crystal recovery from the residual flux Was solved by different methods based on liquid flux elimination at the end of the growth process.:The chemical composition and the homogeneity within the crystals were determined by electron probe micro-analysis and X-rays. Optical (polarized light microscope) and dielectric measurements were used for the characterization and determination of phase transitions, in single crystal with and without an electric field.

Piezoelectric response nonlinearity is approached using the Preisach description of hysteretic systems as collection of distributed bistable units. The Preisach model and its recent physical interpretation in terms of moving domain wall in a stochastically described pinning field are reviewed. It is shown that such an approach can effectively render not only the piezoelectric coefficient field dependences but also the field-response hysteresis, especially in the well-known case of linear piezoelectric field dependence (i.e., Rayleigh’s law) where the bistable units are distributed homogeneously. New expressions for piezoelectric nonlinear behavior departing from the classical linear dependence are then derived using a more complex distribution and are qualitatively compared to experimental data for piezoelectric materials as varied as lead titanate, strontium bismuth titanate, and lead zirconate titanate. Finally, these expressions are shown to be adequate for the description of various piezoelectric coefficient behaviors such as: polynomial dependence on the applied field, dc field effect on nonlinear contributions, and threshold field for nonlinearity.

The Preisach approach was used to describe the widely observed quadratic field dependence of the direct longitudinal piezoelectric coefficient and its associated hysteresis loop. In this perspective, a four parameters distribution function was put forward and refined experimentally using bias stress variations. It permitted one to fully describe the stress bias dependence of the nonlinear coefficients. Considering the hysteresis loop associated with the proposed distribution function, modeling of the experimental data was made possible by the addition of a viscous term. Moreover, the distribution parameters extracted from the loops were in strict agreement with the values obtained either directly from experiments or from bias stress dependence characterization. This new set of results is considered as a further confirmation of the applicability of the Preisach model to piezoelectricity.

Based on direct and converse piezoelectric measurements, our results for relaxor-ferroelectric solid solutions 0.5 Pb(Zr, Ti)O-3-0.5 Pb(Ni1/3Nb2/3)O-3 (PNN-PZT) show that piezoelectric hysteresis can be better described by a coupled Rayleigh-frictional model rather than by either model separately. The nonlinear parameters yielded by such loop analysis are in a good agreement with the ones obtained from piezoelectric nonlinearity, constituting a new validation of Rayleigh-inspired models for the piezoelectric response in ferroelectrics. Finally, the possible mechanisms leading to hysteresis formation are discussed.

The domain wall contributions to the piezoelectric and dielectric properties of ferroelectric materials are discussed in the framework of the Preisach approach. Several examples of the nonlinear behavior in ferroelectric ceramics, thick and highly oriented thin films are discussed

A modified processing method for lead nickel niobate–lead zirconate titanate (Pb(Ni 1/3 Nb 2/3 )O 3 –Pb(Zr,Ti)O 3 , PNN–PZT) solid solutions is presented. This method is based on the high‐temperature synthesis of a precursor that contains all the B‐site cations (Ti, Zr, Ni, and Nb). This synthesis yields a diphasic mixture that contains a ZrTiO 4 ‐like phase and a rutile‐like phase. Both phases exhibit a cationic valence of 4; thus, it is concluded that the mixing of Ni and Nb cations is adequate for the preparation of PNN–PZT solid solutions. Indeed, a pure perovskite phase has been obtained after calcination with lead oxide for compositions that contain 40 and 50 mol% PNN. Moreover, their electromechanical properties have been shown to be superior to values reported for standard columbite routes. This conclusion has been interpreted in terms of enhanced chemical homogeneity.

Losses in piezoelectrics are approached by considering a description of direct stress–charge displacement hysteresis. Shortcomings of the usual loss models (viscous and Rayleigh, taken separately) are briefly demonstrated. Then, a mixed model for piezoelectric losses superimposing viscous and Rayleigh types of descriptions is proposed and validated for a modified lead titanate and lead zirconate titanate (PZT). It is shown for PZT that viscous and Rayleigh-like loss contributions can be effectively separated by fitting the piezoelectric hysteresis loop with an expression combining the two lossy responses. The possibility to obtain all the necessary parameters that describe piezoelectric stress nonlinearity from one single piezoelectric loop is also demonstrated in the case of PZT. The origins of the mixed loss behavior are interpreted as arising from domain wall motion in terms of internal friction mechanisms and of pinning energy ranges.

The Preisach approach is applied to model ferroelectric pinched (or constricted) loops. Starting from the existence of distributed switchable dipolar defects in the material and a corresponding distribution function, an analytical expression for the resulting ferroelectric loop is obtained. The corresponding hysteresis shape is indeed showing a clear pinching. Considerations about defect distribution expression and ways to characterize it from the loop are also made. It is finally suggested that such a description can be applied to any system exhibiting a pinched loop.

The piezoelectric properties of rhombohedral relaxor-ferroelectric compositions close to morphotropic phase boundary have been studied as a function of temperature. As they exhibit, upon heating, a rhombohedral to tetragonal phase transition the piezoelectric behavior changed with temperature. Large piezoelectric (d(33)) and coupling (k(33)) coefficients of 0.91 Pb(Zn1/3Nb2/3)O-3-0.09PbTiO(3) single crystals drop to usual ceramic values after crossing the transition. Intrinsic and reversible contributions to the piezoelectric response reach a maximum at transition for 0.50PNN-0.16PZ-0.34PT. The influence of poling temperature on extrinsic contributions through possible structural changes was demonstrated.