Electric-Field-Driven Coexistence Of Positive And Negative Electrocaloric Effects Near Room Temperature For High-Efficiency Two-Stage Cooling

The electrocaloric (EC) effect is promising for the next-generation solid-state refrigeration, yet it is difficult to improve the EC response near room temperature with either the positive electrocaloric (PEC) or negative electrocaloric (NEC) effect alone. In this work, we propose and demonstrate a strategy that achieves the coexistence of PEC and NEC effects near room temperature via electric-field-induced ferroelectric-ferroelectric phase transition in Ba(ZrxTi1-x)O-3 solid solutions, while the PEC effect is generally found around paraelectric-ferroelectric transition and the NEC effect is around ferroelectric-antiferroelectric phase boundaries. Utilizing such a coexistence of PEC and NEC effects, we propose a prototype two-stage cooling device, wherein both the EC cooling temperature change and efficiency are higher than its counterpart with only the PEC or NEC effect, offering a new pathway for EC cooling in practical applications near room temperature.