The pyroelectric energy harvesting capabilities of PMN–PT near the morphotropic phaseboundary

Abstract

This paper reports on direct thermal to electrical energy conversion by performing the Olsen cycleon pyroelectric materials. The energy harvesting capability of commercially available [001] oriented68PbMg1/3Nb2/3O3–32PbTiO3 (PMN–32PT) single crystal capacitors was measured experimentally. An energy density of 100 mJ cm−3/cycle, correspondingto 4.92 mW cm−3, was obtained by successively dipping the material in oil baths at temperatures 80 and170 °C and cycling the electric field between 2 and 9 kV cm−1. Similarly, an energydensity of 55 mJ cm−3/cycle wasobtained between 80 and 140 °C. An estimated 40% of this energy resulted from the strain polarization due to therhombohedral to tetragonal phase transition. The strain from this transition disappearedwhen the maximum operating temperature exceeded the Curie temperature of about150 °C. Theoptimal low electric field used in the Olsen cycle maximizing the energy harvested was found to be around2 kV cm−1. In addition, the material suffered from (i) dielectric breakdown for electric fields larger than 9 kV cm−1 and (ii) cracking from thermal stress for operating temperature differences in excess of90 °C. A physical model predicting the total amount of energy harvested was also derived,accounting for thermal expansion as well as temperature dependent dielectricconstant and spontaneous polarization. The model predictions fell within20% of the experimental results in the temperature range between 80 and170 °C and electric fieldsranging from 2 to 9 kV cm−1.