  The electrocaloric effect (ECE) offers a promising alternative to the
traditional gas compressing refrigeration due to its high efficiency and
environmental friendliness. The unusual negative electrocaloric effect refers
to the adiabatic temperature drops due to application of electric field, in
contrast with the normal (positive) ECE, and provides ways to improve the
electrocaloric efficiency in refrigeration cycles. However, negative ECE is
unusual and requires a clear understanding of microscopic mechanisms. Here, we
found unexpected and extensive negative ECE in nonpolar orthorhombic,
tetragonal, and cubic phases of halide and oxide perovskite at wide range of
temperature by means of first-principle-based large scale Monte Carlo methods.
Such unexpected negative ECE originates from the octahedral tilting related
entropy change rather than the polarization entropy change under the
application of electric field. Furthermore, a giant negative ECE with
temperature change of 8.6 K is found at room temperature. This giant and
extensive negative ECE in perovskite opens up new horizon in the research of
caloric effects and broadens the electrocaloric refrigeration ways with high
efficiency.
