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.
Pulsed capacitors require high energy density and low loss, properties that can be realized through selection of composition. Ceramic (Pb0.88La0.08)(Zr0.91Ti0.09)O3 was found to be an ideal candidate. La3+ doping and excess PbO were used to produce relaxor antiferroelectric behavior with slim and slanted hysteresis loops to reduce the dielectric hysteresis loss, to increase the dielectric strength, and to increase the discharge energy density. The discharge energy density of this composition was found to be 3.04 J/cm3 with applied electric field of 170 kV/cm, and the energy efficiency, defined as the ratio of the discharge energy density to the charging energy density, was 0.920. This high efficiency reduces the heat generated under cyclic loading and improves the reliability. The properties were observed to degrade some with temperature increase above 80 °C. Repeated electric field cycles up to 10 000 cycles were applied to the specimen with no observed performance degradation.
Relaxor ferroelectric single crystals have triggered revolution in electromechanical systems due to their superior piezoelectric properties. Here the results are reported on experimental studies of energy harvested from (1-y-x)Pb(In1/2Nb1/2)O3–(y)Pb(Mg1/3Nb2/3)O3–(x)PbTiO3 (PIN-PMN-PT) crystals under high strain rate loading. Precise control of ferroelectric properties through composition, size and crystallographic orientation of domains made it possible to identify single crystals that release up to three times more electric charge density than that produced by PbZr0.52Ti0.48O3 (PZT 52/48) and PbZr0.95Ti0.05O3 (PZT 95/5) ferroelectric ceramics under identical loading conditions. The obtained results indicate that PIN-PMN-PT crystals became completely depolarized under 3.9 GPa compression. It was found that the energy density generated in the crystals during depolarization in the high voltage mode is four times higher than that for PZT 52/48 and 95/5. The obtained results promise new single crystal applications in ultrahigh-power transducers that are capable of producing hundreds kilovolt pulses and gigawatt-peak power microwave radiation.
Stress-induced and thermal-induced depolarization studies along with X-ray diffraction were performed on lead zirconate titanate ferroelectrics of different compositions, PbZr0.52Ti0.48O3 (PZT 52/48) and PbZr0.95Ti0.05O3 (PZT 95/5). Specimens were shock loaded perpendicular to the polarization vector. It was found that the polarity of the stress-induced charge released by PZT 52/48 and 95/5 was opposite to the polarity of the charge generated due to the piezoelectric effect. PZT 52/48 was only partially (45%) depolarized under 1.5 ± 0.1 GPa mechanical compression, as opposed to PZT 95/5 which was fully depolarized. The experimental results indicate that the stress-induced depolarization mechanisms are different for these two compositions. PZT 52/48 is transformed to a state with lower polarization, while PZT 95/5 undergoes a phase transition to a non-polar antiferroelectric phase.
Ceramic niobium modified 95/5 lead zirconate-lead titanate (PZT) undergoes a pressure induced ferroelectric to antiferroelectric phase transformation accompanied by an elimination of polarization and a volume reduction. Electric field and temperature drive the reverse transformation from the antiferroelectric to ferroelectric phase. The phase transformation was monitored under pressure, temperature, and electric field loading. Pressures and temperatures were varied in discrete steps from 0 MPa to 500 MPa and 25 °C to 125 °C, respectively. Cyclic bipolar electric fields were applied with peak amplitudes of up to 6 MV m−1 at each pressure and temperature combination. The resulting electric displacement–electric field hysteresis loops were open “D” shaped at low pressure, characteristic of soft ferroelectric PZT. Just below the phase transformation pressure, the hysteresis loops took on an “S” shape, which split into a double hysteresis loop just above the phase transformation pressure. Far above the phase transformation pressure, when the applied electric field is insufficient to drive an antiferroelectric to ferroelectric phase transformation, the hysteresis loops collapse to linear dielectric behavior. Phase stability maps were generated from the experimental data at each of the temperature steps and used to form a three dimensional pressure–temperature–electric field phase diagram.
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