Waste heat can be directly converted into electrical energy by performing the Olsen cycle on lanthanum doped lead zirconate titanate (x/65/35 PLZT) ceramics. The Olsen cycle consists of two isothermal and two isoelectric field processes in the electric displacement versus electric field diagram. A maximum energy density of 888 J/L per cycle was achieved 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. A maximum power density of 55 W/L was obtained at 0.125 Hz for operating temperatures between 3 and 140 C and the electric field cycled between 0.2 and 6.0 MV/m. To the best of our knowledge, these are the largest pyroelectric energy and power densities experimentally measured with multiple cycles. The electrical breakdown strength and therefore the energy and power densities of the material increased as the sample thickness was reduced. Furthermore, the electrode material was found to have no significant effect on the energy and power densities for samples subject to the same operating temperatures and electric fields. However, samples with electrode material possessing thermal expansion coefficients similar to that of PLZT were capable of withstanding larger temperature swings. Finally, 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.