Pyroelectric energy conversion using PLZT ceramics and the ferroelectric–ergodic relaxor phase transition

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. (Some figures may appear in colour only in the online journal)