Thermal energy harvesting from Pb(Zn1/3Nb2/3)0.955Ti0.045O3 single crystals phase transitions

This paper describes the effect of the frequency on energy harvesting in Pb(Zn1/3Nb2/3)(0.955)Ti0.045O3 single crystals with an Ericsson cycle. At the lowest frequency of 0.01 Hz (which corresponds to the slope for the application of the electric field), the maximum harvested energy was equal to 86 mJ cm(-3). With an increase in frequency, the harvested energy demonstrated a nonlinear decrease, and the diminution was particularly rapid at frequencies above the critical frequency of 1 Hz. The inherent mechanism of the frequency effect is discussed in detail. In the present case, the phase transitions due to domain engineering, e.g., R-O during the charge process at low temperature and O-T during the discharging process at high temperature, greatly improved the harvested energy. The study also revealed that various parameters, such as the electric field associated with the phase transition, the polarization relaxation, and polarization variations, influenced the capability of energy harvesting to a certain extent. This capability depended significantly on the electric field frequency. Especially at high frequency, the reduction in the polarization time resulted in an inadequate phase transition, and subsequently gave rise to the coexistence of orthorhombic and rhombohedral phases. This had an adverse effect on the energy harvesting, and consequently, the harvested energy exhibited a decreasing tendency with an increasing electric field. Based on the result of the frequency effect, two asymmetric Ericsson cycles were attempted: an L-H cycle and an H-L cycle. These cycles employed different imposed frequencies at the charge and the discharge of the sample. Both asymmetric cycles agreed well with the performed analysis on the influence of the frequency. The H-L cycle greatly promoted energy harvesting, and its harvested energy reached 106 mJ cm(-3), thus corresponding to the most effective energy harvesting cycle for this material.