Strong electrocaloric response with ultrawide working temperature span in lead-free BaTiO3-based ceramics by composition design

Solid-state refrigeration technology based on electrocaloric effect provides a cost-effective and convenient approach for microelectronic device cooling. However, the working temperature range of electrocaloric materials is often narrow and incommensurate with that required by many microelectronic devices including computer chips and CPUs. In this work, the working temperature span of electrocaloric response in BaTiO3 ceramics were tuned by the simultaneous introduction of Sr and Hf (abbreviated as BSHT). Through rational variation of Sr and Hf content, not only the Curie temperature is reduced to ∼80 °C, but also the room-temperature phase structure of the ceramics can be effectively tuned from a single rhombohedral phase to coexistence of rhombohedral + orthorhombic or orthorhombic + tetragonal phases. Relaxor behavior of BSHT ceramics is evident by the frequency-dispersion of dielectric permittivity and the increased relaxor diffuseness factor γ. Temperature-dependent Raman spectra confirm that Ba0.85Sr0.15Hf0.06Ti0.94O3 (0.6BSHT) sustain a two-phase coexistence state over a broad temperature range. 0.6BSHT ceramics render a large adiabatic temperature change ΔT of 0.91 K under 40 kV cm−1 with a broad temperature span of ∼57 °C, covering the working temperature window of most microelectronic devices. Moreover, the electrocaloric response of 0.6BSHT shows excellent fatigue endurance, i.e., the adiabatic temperature change shows a trivial degradation of <4.4 % after 106 cycles. This work demonstrates that BaTiO3-based ceramics remain one of the most promising electrocaloric candidates and compositional modification is an effective route to tune the electrocaloric response for fulfilling the requirements of practical applications.