To investigate how exhaust heat from automobiles can be converted to renewable energy, an innovative electrothermodynamic cycle is presented, which is based on temporal temperature variations, the pyroelectric effect, instead of spatial temperature gradient, and the Seebeck effect. A generating mechanism is investigated using operando time‐resolved synchrotron X‐ray diffraction. Practical energy and true energy breakeven are achieved via real engine dynamometer experiments.

A novel electrothermodynamic cycle based on temporal temperature variations (dT/dt); the pyroelectric effect was investigated for its potential role in the use of waste heat as renewable energy. Here, we present improved generating performance with relaxer ferroelectric ceramics ((1-x)Pb(Mg_2/3Nb_1/3)O₃-xPbTiO₃ (PMN-xPT)), which are well known for their strong dielectric and pyroelectric properties near the morphotropic phase boundary. The theoretical potential was evaluated using hysteresis loops, and the generating properties were analyzed in the laboratory using an engine dynamometer. The experiments yielded a value of 0.48 mW/cm³, which is 3 times larger than that obtained previously, because of the high polarization properties.

In pyroelectric applications, the general figures of merit (FOMs) have been applied and reported near room temperature. We derived the modified FOMs in considering our electro‐thermodynamic cycle for the usage environment of automotive applications. The relationship between the material properties and generating performance of PZTs was investigated at various temperatures. The was suggested from F_D, a FOM for a pyroelectric sensor, based on the modified pyroelectric coefficient (p); . was calculated by the change of the spontaneous polarization (P_S) according to a given temperature variation during one cycle; ΔP_S/ΔT (T_max−T_min). It was indicated that the could be effective as a FOM for the pyroelectric generating performance and the dielectric loss (tanδ ) significantly affected the generating performance in addition to under high‐temperature and electric field conditions. Furthermore, of the PZTs tested, C‐91 sample which showed the highest generating performance resulted in a generating energy of 1.3 mW cm^–3 in the engine dynamometer assessment. This is 13 times greater than the generating energy reported in a previous study of C‐6 (0.1 mW cm^–3).

The effects of CaO content and post-heat treatment were investigated on the phase stability and mechanical and thermal properties of Ca-PSZ. ZrO₂ specimens with 5–10 mol% CaO were sintered, and post-heat treatment was performed at 1200 °C for 100 h. Subsequently, to test and analyze the crystal structure and the microstructure, the mechanical and thermal properties of the specimens were evaluated. All specimens were partially stabilized by 5–10 mol% CaO (5CSZ–10CSZ) in a mixed monoclinic and tetragonal phase; however, peaks of the secondary phase of CaZrO₃ were observed in 10CSZ. The ratio of the monoclinic phase decreased from 62.50% (5CSZ) to 21.02% (10CSZ) as the CaO content increased. Additionally, the monoclinic phase ratio decreased from 59.38% (5CSZ) to 19.57% (9CSZ) after the post-heat treatment; an increase to 24.84% was observed for 10CSZ. An increase in Vickers hardness from 676.02 to 1256.25 HV and flexural strength from 437.7 to 842.7 MPa was observed with increasing CaO content. The post-heat treatment resulted in further increases in these values as the CaO content increased from 5CSZ to 9CSZ; however, the Vickers hardness and flexural strength of 10CSZ decreased by approximately 8% and 9%, respectively. The thermal expansion coefficient exhibited the same tendency as the mechanical properties. This coefficient increased from 8.229 × 10⁻⁶ to 9.448 × 10⁻⁶ K⁻¹ with increasing CaO content and was enhanced after the post-heat treatment in 5CSZ to 9CSZ; however, the thermal expansion coefficient of 10CSZ decreased by approximately 4% after the post-heat treatment. The mechanically and thermally stable tetragonal phase increased, and the monoclinic phase decreased as the doped Ca replaced the Zr sites, as was confirmed by the X-ray diffraction (XRD) analysis. The post-heat treatment and the increased Ca addition further facilitated the replacement of Zr sites by Ca. However, at high Ca concentrations of 10CSZ, an equilibrium phase of CaZrO₃ was formed as a secondary phase at the post-heat treatment temperature, resulting in low performance.

The phase formation and stabilization behaviors of calcia partially stabilized zirconia (Ca-PSZ) were investigated with regard to the CaO content and post-heat treatment. Sintered specimens were prepared by adding 2, 3, 4, and 5 mol% to CaO to ZrO₂, and post-heat treatment were conducted. In the X-ray diffraction pattern, the monoclinic peak decreased, the tetragonal peak increased upon CaO doping, and no CaZrO₃ peak was observed. Transmission electron microscopy images of the Ca-PSZ showed that the d-spacing of 4CSZ (200)_m extended from 0.260 nm to 0.266 nm subsequent to post-heat treatment. The coefficient of thermal expansion gradually increased in accordance with the dopant concentration, in addition, it increased even after the post-heat treatment. These results are related to the increase in tetragonal phase, which has a relatively higher coefficient of thermal expansion than that of the monoclinc phase. According to the Vickers hardness measurement, the hardness of all specimens increased gradually as the concentration of CaO increased, and the hardness of the 5CSZ was improved from 676 to 774 Hv by the post-heat treatment.