Room Temperature Electrocaloric Effect in 2D Ferroelectric CuInP$_2$S$_6$ for Nano-refrigerators.

A material with reversible temperature change capability under an external electric field, known as the electrocaloric effect (ECE), has long been considered as a promising solid-state cooling solution. However, electrocaloric (EC) performance of EC materials generally is not sufficiently high for real cooling applications. As a result, exploring new EC materials with high performance is of great interest and importance. Here, we report on the ECE of a new class of EC material, the 2D ferroelectric materials (CuInP$_2$S$_6$ or CIPS in this work in particular) for the first time. Over 60% polarization charge change is observed within a temperature change of only 10 K at Curie temperature, as the result of a second order phase transition in CIPS. Large adiabatic temperature change (|{Delta}T|) of 3.5 K, isothermal entropy change (|{Delta}S|) of 6.1 J kg$^{-1}$ K$^{-1}$ at |{Delta}E|=142.0 kV cm$^{-1}$ at 315 K (above and near room temperature) are achieved, with a large EC strength (|{Delta}T|/|{Delta}E|) of 29.2 mK cm kV$^{-1}$. The ECE of CIPS is also investigated theoretically by numerical simulation and a further EC performance projection is provided.