Substantially Enhanced Electrocaloric Effect in Ba(Zr0.2Ti0.8)O3 Lead- Free Ferroelectric Ceramics via Lattice Stress Engineering

As an alternative to conventional vapor-compression refrigeration, cooling devices based on electrocaloric (EC) materials are environmentally friendly and highly efficient, which are promising in realizing solid-state cooling. Lead-free ferroelectric ceramics with competitive EC performance are urgently desirable for EC cooling devices. In the past few decades, constructing phase coexistence and high polarizability have been two crucial factors in optimizing the EC performance. Different from the external stress generated through heavy equipment and inner interface stress caused by complex interface structures, the internal lattice stress induced by ion substitution engineering is a relatively simple and efficient means to tune the phase structure and polarizability. In this work, we introduce low-radius Li+ into BaZr0.2Ti0.8O3 (BZT) to form a particular A-site substituted cell structure, leading to a change of the internal lattice stress. With the increase of lattice stress, the fraction of the rhombohedral phase in the rhombohedral- cubic (R-C) coexisting system and ferroelectricity are all pronouncedly enhanced for the Li2CO3-doped sample, resulting in the significant enhancement of saturated polarization (Ps) as well as EC performance [e.g., adiabatic temperature change (Delta T) and isothermal entropy change (Delta S)]. Under the same conditions (i.e., 333 K and 70 kV cm-1), the Delta T of 5.7 mol % Li2CO3-doped BZT is 1.37 K, which is larger than that of the pure BZT ceramics (0.61 K). Consequently, in cooperation with the great improvement of electric field breakdown strength (Eb) from 70 to 150 kV cm-1, 5.7 mol % Li2CO3-doped BZT achieved a large Delta T of 2.26 K at a temperature of 333 K, which is a competitive performance in the field of electrocaloric effect (ECE). This work provides a simple but effective approach to designing high-performance electrocaloric materials for next-generation refrigeration.

Automated summary

This study introduces low-radius Li+ into BaZr0.2Ti0.8O3 (BZT) through ion substitution engineering, leading to a change in internal lattice stress and a significant enhancement of the ferroelectric properties in BZT ceramics. Under the conditions of 333 K and 70 kV cm-1, the adiabatic temperature change of 5.7 mol% Li2CO3-doped BZT is 1.37 K, which is higher than that of pure BZT ceramics (0.61 K). Therefore, this work provides a simple but effective approach to design high-performance electrocaloric materials for next-generation refrigeration.