Coexistence of large positive and negative electrocaloric effects near room temperature in a Pb1−x(Li,La)xZrO3/Ca3Mn2O7 heterojunction†

Electrocaloric refrigeration films have a very significant potential for application in the field of microelectronics. However, it is difficult for the refrigeration efficiency of a single positive/negative electrocaloric effect to match the demand, because it can only cool when the electric field is removed or applied. Herein, the coexistence of large positive and negative electrocaloric effects is obtained in a Pb_1−x(Li_0.5La_0.5)_xZrO₂/Ca₃Mn₂O₇ (PLLZ/CMO) heterojunction near room temperature. The built-in electric field is induced in the heterojunction region, and it can regulate the phase structure of the PLLZ layer in the heterojunction region with the help of the external electric field. In addition, Li⁺–La³⁺ doping suppresses the phase transition of the PLLZ layer, and thus the change in the sign of the temperature is regulated by the external electric field. The adiabatic temperature changes of the PLLZ/CMO bilayer film with x = 0.4 at 303 K are 33 K at 550 kV cm⁻¹ and −1.54 K at 140 kV cm⁻¹. The large positive and negative temperature changes regulated by the voltage indicate a reliable technique for practical production.