Waste heat can be directly converted into electrical energy by performing the Olsen cycle on pyroelectric materials. The Olsen cycle consists of two isothermal and two isoelectric field processes in the electric displacement versus electric field diagram. This paper reports on the electrical energy generated by lanthanum-doped lead zirconate titanate (8/65/35 PLZT) subjected to the Olsen cycle. The material was alternately dipped into a cold and a hot silicone oil bath under specified electric fields. A maximum energy density of 888 J l −1 /cycle was obtained with a 290 µm thick 8/65/35 PLZT sample for temperatures between 25 and 160 • C and electric fields cycled between 0.2 and 7.5 MV m −1. To the best of our knowledge, this is the largest pyroelectric energy density experimentally measured with multiple cycles. It corresponded to a power density of 15.8 W l −1. The electrical breakdown strength and therefore the energy and power densities of the material increased as the sample thickness was reduced from 720 to 290 µm. Furthermore, a physical model for estimating the energy harvested by ferroelectric relaxors was further validated against experimental data for a wide range of electric fields and temperatures.

This paper is concerned with direct conversion of waste heat into electricity by executing the Olsen cycle on lead lanthanum zirconate titanate (PLZT) ceramics undergoing a relaxor-ferroelectric phase transition. The Olsen cycle consists of two isothermal and two isoelectric field processes. First, the temperature-dependent dielectric properties were measured for x/65/35 PLZT. The polarization transition temperature of x/65/35 PLZT was found to decrease from 240 to 10 • C as x increased from 5 to 10 mol%. This suggests that the different compositions should be operated over different temperature ranges for maximum thermal to electrical energy conversion. The energy and power densities generated by the Olsen cycle using x/65/35 PLZT samples were measured by successively dipping the samples in isothermal dielectric oil baths. Large energy and power densities were obtained when the samples underwent the ergodic relaxor-ferroelectric phase transition. A maximum energy density of 1014 J l −1 per cycle was obtained with a 190 µm thick 7/65/35 PLZT sample cycled at 0.026 Hz between 30 and 200 • C and between 0.2 and 7.0 MV m −1 . To the best of our knowledge, this is the largest pyroelectric energy density ever demonstrated experimentally with ceramics, single crystals, or polymers. A maximum power density of 48 W l −1 was achieved using a 200 µm thick 6/65/35 PLZT sample for temperatures between 40 and 210 • C and electric fields between 0 and 8.5 MV m −1 at a frequency of 0.060 Hz. The maximum applied electric field and temperature swings of these materials were physically limited by dielectric breakdown and thermomechanical stress.

No abstract