Colossal room-temperature electrocaloric strength aided by hydrostatic pressure in lead-free multiferroic solid solutions

Abstract: Solid-state cooling applications based on the electrocaloric (EC) effect are particularly promising from a technological point of view due to their downsize scalability and natural implementation in circuitry. However, EC effects typically occur far from room temperature, involve materials that contain toxic substances and require relatively large electric fields ($\sim 100$-$1000$ kV cm$^{-1}$) that cause fateful leakage current and dielectric loss problems. Here, we propose a possible solution to these practical issues that consists in concertedly applying hydrostatic pressure and electric fields on lead-free multiferroic materials. We theoretically demonstrate this strategy by performing first-principles simulations on supertetragonal BiFe${1-x}$Co${x}$O$_{3}$ solid solutions (BFCO). It is shown that hydrostatic pressure, besides adjusting the occurrence of EC effects to near room temperature, can reduce enormously the intensity of the driving electric fields. For pressurized BFCO, we estimate a colossal room-temperature EC strength, defined like the ratio of the adiabatic EC temperature change by the applied electric field, of $\sim 1$ K cm kV$^{-1}$, a value that is several orders of magnitude larger than those routinely measured in uncompressed ferroelectrics.