The alteration of the high-field electrical permittivity (nonlinear response) of PZT-based ceramics when an electrical bias field is applied is reported in this work. Large differences are observed between soft and hard PZT behaviours. While in soft PZT a bias field does not modify the nonlinear behaviour, a notable dependence is verified in hard PZT. The Preisach model is satisfactorily used to describe experimental results. A distribution function containing the first terms of the Maclaurin development series of a function composed by two Gaussian-like functions of different amplitudes is proposed. The model gives a satisfactory explanation for the fact that the permittivity depends not only on the amplitude of the applied electric field, but also on the bias field, both for soft and hard ceramics and for poled or unpoled samples.

A uniaxial compressive stress significantly modifies the dielectric and piezoelectric response of Pb(Zr,Ti)O3 (PZT)-based piezoceramics. In soft PZT, the pre-stress decreases both the piezoelectric coefficient and its increment with increasing dynamical stress amplitude. However, an increase of both quantities is shown in hard PZT. Similar effects are observed in the dielectric response. It is proposed that the differences between such behaviors are due to the possibility of domain coalescence in the materials whose domain walls have high mobility. Furthermore, the enhancement of the response in hard PZT could be explained by change of the interaction energy between complex defects and domain walls induced by the compression.

By their ferroelectric nature, ferro-piezoelectric ceramics have a non-linear behaviour. This nature is reinforced by their notably complex grain and domain structure, which leads to a less linear behaviour than is expected for a single crystal.

This paper presents an investigation on dielectric and mechanical nonlinear properties in Mn-doped PMN-35PT ceramics. The structural study of the ceramics verifies that the 1% mol Mn doped PMN-35PT is a pure perovskite phase with a tetragonal symmetry. SEM micrograph shows the same microstructural mor- phology of an undoped ceramic. From the EPR spectra, it has been concluded that the major part of Mn is present in Mn2+ rather than in Mn4+ form. The addition of Mn2+ ions acts on the dielectric, piezoelectric and mechanical properties by decreasing the relative dielectric permittivity (3800 to 2074), the dielectric losses (0.60 to 0.53), the piezoelectric coefficient d33 (650 to 403 pC/N), and increasing the mechanical quality fac- tor Qm (78 to 317). It was found that in Mn2+ doped ceramics the dielectric response can not be described by Rayleigh law. This result can be understood taking into account that reversible motion of the domain wall is a relevant contribution to response of this material.

In this work, the contribution of the extrinsic effect to the macroscopic properties in soft and hard lead zirconate titanate ceramics is directly evaluated. Close to the room temperature, poled hard ceramics show an anomalous behavior, which is notably different from that of soft ceramics, not only in dielectric but also in piezoelectric and elastic responses. Hence, at room temperature their properties are thermally stable and the losses are unusually low. It is suggested that two mechanisms are present, with one mechanism inhibiting the other.

A system of nonlinear measurement and nonlinear elastic characterization of resonators is presented, which increases the possibilities and characteristics of the other classic nonlinear characterization methods. This characterization has been necessary due to the use of resonators in power devices, where their behavior departs from the linear characteristics. The use of burst signals and a system of acquisition and data processing is proposed instead of impedance analyzers, thus avoiding the thermal effects associated with the high-signal measures, which are necessary for this characterization. The measures are repeated for different amplitudes and at the same frequency near the resonance by a single amplitude sweep, which is simpler and faster to carry out than the multiple frequency sweepings used in other methods. As a last resort, a variation on the proposed method, closer to the classical measures, is put forward, in which the resonance is ensured in all the measures. Special emphasis is placed on obtaining nonlinear characterization of the piezoceramic material in order to increase its optimization in the transducers in terms of both its use and its composition and structure.

The structure of medium-grain piezoelectric ceramics often consists of alternate lamellae of non-180° domains. In this work, the extrinsic effects of the electric and elastic fields on such structures are studied. A description of the extrinsic behavior of a single grain is given, and it is shown that the relations between piezoelectric and dielectric or elastic constants must be independent of the wall mobility, being solely dependent on the relation between spontaneous polarization and strain. By using an appropriate coordinate system, the conditions under which the intrinsic and extrinsic effects can be added are analyzed. The linear global behavior of a grain can then be described as a function of its orientation and of two additional parameters: the lack of equilibrium between domains α and its mean thickness d. The basis is established to describe the state of a ceramic through a distribution function that accounts for domain orientation and which depends on the poling, fatigue, and ageing of the sample. Finally, the goodness of the model is analyzed, although some aspects must be still modified in order to describe the overall behavior of the ceramic.

Non-linear increases in elastic, piezoelectric (direct and reverse) and dielectric coefficients have been measured under a high electrical field or under high mechanical stress. The permittivity and reverse piezoelectric coefficient can be measured by applying a high voltage at a low frequency, while the elastic compliance and direct piezoelectric coefficient can be measured at the first radial resonance frequency in order to apply a high stress. The non-linear behaviour has been analysed at the radial resonance of a disc. In all the materials tested, the results show that there is a close relation between the non-linear increments of the different coefficients. An empirical model has been proposed in order to describe and understand these relations. It is assumed that either the strain or the electrical displacement is produced by intrinsic and extrinsic processes, but only the latter, which consist mainly in the motion of domain walls, contribute to the non-linearity. The model enables us to find the domain wall contribution to elastic, piezoelectric and dielectric non-linearities, and allows us to compare the amplitudes of the fields and stresses that produce the same displacement of domain walls.