Stress and electric field induced phase transitions for ultra high energy conversion in ferroelectrics

This work focuses on energy harvesting of ferroelectric relaxors PMN-25PT and PZN-8PT single crystals with high uniaxial stress and electric field. Ericsson cycle, which consists of applying and releasing electric field and stress at different steps of the cycle, has been used. A large energy density for PZN-8PT high as 410 mJ/cm3 was obtained. Different working temperatures were tested by experiment and modeled via Landau-Devonshire theory. Optimal working temperatures were identified for high level energy conversion and were successfully predicted by simulation. It appeared that the optimum working temperature was different from that optimizing the d33. Polarization mechanisms induced by these extreme conditions for energy harvesting are explained in the frame of experimental and modeling results. The results obtained at high stress levels tend to indicate that operating along the polarization direction yields the best results, which contradicts conclusions drawn in the case of domain engineered crystals.