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The possibility of recycling ambient energies with electric generators instead of using batteries with limited life spans has stimulated important research efforts over the past years. The integration of such generators into mainly autonomous low-power systems, for various industrial or domestic applications is envisioned. In particular, the present work deals with energy harvesting from mechanical vibrations. It is shown here that direct piezoelectric energy harvesting (short circuiting on an adapted resistance, for example) leads to relatively weak energy levels that are insufficient for an industrial development.

The temperature dependence of the piezoelectric properties of 0.67Pb (Mg1 / 3Nb$_{2 / 3})$O3-0.33PbTiO3and 0.955Pb(Mg1 / 3Nb$_{2 / 3})$O3-0.045PbTiO3single crystals, respectively grown by Bridgman and modified Bridgman method was investigated. Due to their low rhombohedral to tetragonal transition temperature and Curie point (Tc= 152oC and 166oC), the properties of these single crystals have an unstable behavior as soon as the first transition temperature is reached, i.e. the piezoelectric coefficients exhibit a non linear or a hysteretic behavior during temperature cycle.
The objective of this paper is to study the thermal stability of piezoelectric and dielectric coefficients for the two compositions in order to point out the limiting factors in term of transducers performances and to explain the observed behavior.

The possibility of recycling ambient energies with electric generators instead of using batteries with limited life spans has stimulated important research efforts over the past years. The integration of such generators into mainly autonomous low-power systems, for various industrial or domestic applications is envisioned. In particular, the present work deals with energy harvesting from mechanical vibrations. It is shown here that direct piezoelectric energy harvesting (short circuiting on an adapted resistance, for example) leads to relatively weak energy levels that are insufficient for an industrial development. By coupling an electric field and mechanical excitation on Ericsson-based cycles, the amplitude of the harvested energy can be highly increased, and can reach a maximum close to 100 times its initial value. To obtain such a gain, one needs to employ high electrical field levels (high amplitude, high frequency), which induce a non-linearity through the piezoceramic. A special dynamic hysteresis model has been developed to correctly take into account the material properties, and to provide a real estimation of the harvested energy. A large number of theoretical predictions and experimental results have been compared and are discussed herein, in order to validate the proposed solution.