Influence of grain size on the electrocaloric and pyroelectric properties in non-reducible BaTiO3 ceramics

The present work demonstrates the effect of the grain size on electrocaloric and pyroelectric properties in BaTiO3-based ceramics prepared by a chemical coating method and then sintered in a reducing atmosphere at different temperatures. In a grain size of 136 ± 50 nm to 529 ± 245 nm, the electrocaloric temperature change increases from 0.30 K to 0.63 K under the electric field of 4 MV/m at the ferroelectric–paraelectric phase transition. The corresponding entropy change, heat extraction capacity, coefficient of performance, and electrocaloric strength exhibit a twofold increase (i.e., 0.31 J/kg K–0.75 J/kg K, 148 J/kg–303 J/kg, 7–14, and 0.0075 K cm/kV–0.016 K cm/kV, respectively). The effects of the grain size on the pyroelectric properties are established from the pyroelectric coefficient and the associated pyroelectric figures of merit (FOMs). The pyroelectric coefficient and pyroelectric FOMs exhibit about a fivefold increase with the increasing grain size. The pyroelectric energy harvesting is calculated for the Olsen cycle. The energy harvesting capabilities enhance from ∼96 kJ/m3 to ∼135 kJ/m3 when the cycle is operated at temperatures between 303 K and 423 K and an electric field between 1 MV/m and 4 MV/m. The results show that the increase in the grain size significantly improves the electrocaloric and pyroelectric properties. Furthermore, it is established that the pyroelectric properties are more sensitive to the grain size as compared to the electrocaloric effect when ceramics are prepared by the chemical coating-cum-sintering route. In summary, the present study suggests that microstructure control in BaTiO3 fabrication with the enhanced grain size can be an effective approach to enhance the pyroelectric and electrocaloric properties.