Electrocaloric Effect of Sm-Doped 0.5BZT–0.5BCT Lead-Free Ceramics

Abstract

The use of refrigeration technology is widespread in national security, industrial and agricultural production, biomedicine, and everyday life. High efficiency, environmental friendliness, and low cost make solid-state refrigeration based on electrocaloric effect (ECE) a promising refrigeration technology. Lead-free ferroelectric ceramics (1–x)Ba(Zr_0.2Ti_0.8)O₃–x(Ba_0.7Ca_0.3)TiO₃ (BZT–BCT) are promising materials for electrocaloric refrigeration in the field. In this paper, Sm-doped 0.5BZT–0.5BCT ceramic was fabricated by the conventional solid-state reaction method. The effect of Sm-doping contents (0, 1.0, 2.0, 2.5, and 3.0 mol.%) on the phase structures, dielectric properties, ferroelectricity, and electrocaloric properties of 0.5BZT–0.5BCT ceramics was systematically examined. The results indicate that all ceramics have a pure perovskite structure with no other secondary phase available. High relative densities are observed in all lead-free ferroelectric ceramics and all of the samples show transgranular fracture with no clear grain boundaries seen. The ceramics’ ferroelectric hysteresis loops become thinner as the Sm doping content increases. At that, remanent polarization Pr decreases, indicating that more polar nanoregions (PNRs) are formed in BZT–BCT lead-free ceramics through Sm doping. The increase in Sm doping content resulted in a change in the dielectric permittivity and electrocaloric temperature that first increased and then decreased. The maximum dielectric permittivity is 5,518 when the doping content of Sm is 2.5 mol.% and the maximum electrocaloric temperature change ΔT_max of 0.109 K at 4 kV/mm was obtained when Sm doping content was 2 mol.%. The results show that an appropriate Sm doping is favorable for improving the dielectric, ferroelectric, and electrothermal properties of lead-free ceramics 0.5BZT–0.5BCT.