The strain-induced transitions of the piezoelectric, pyroelectric and electrocaloric properties of the CuInP$_2$S$_6$ films

TL;DR

This study investigates how strain influences the piezoelectric, pyroelectric, and electrocaloric properties of CuInP$_2$S$_6$ thin films, revealing an unusual strain response opposite to typical ferroelectric materials, with implications for nanoscale device applications.

Contribution

It demonstrates the strong, strain-dependent behavior of ferroelectric properties in CuInP$_2$S$_6$ films, highlighting an anomalous response to mismatch strain unlike other ferroelectrics.

Findings

Mismatch strain significantly alters ferroelectric responses.

Sign of strain determines the behavior of properties.

Unusual strain effects are opposite to typical ferroelectric films.

Abstract

The low-dimensional ferroelectrics, ferrielectrics and antiferroelectrics are of urgent scientific interest due to their unusual polar, piezoelectric, electrocaloric and pyroelectric properties. The strain engineering and strain control of the ferroelectric properties of layered 2D Van der Waals materials, such as CuInP$_2$(S,Se)$_6$ monolayers, thin films and nanoflakes, are of fundamental interest and especially promising for their advanced applications in nanoscale nonvolatile memories, energy conversion and storage, nano-coolers and sensors. Here, we study the polar, piezoelectric, electrocaloric and pyroelectric properties of thin strained films of a ferrielectric CuInP$_2$S$_6$ covered by semiconducting electrodes and reveal an unusually strong effect of a mismatch strain on these properties. In particular, the sign of the mismatch strain and its magnitude determine the complicated behavior of piezoelectric, electrocaloric and pyroelectric responses. The strain effect on these properties is opposite, i.e., "anomalous", in comparison with many other ferroelectric films, for which the out-of-plane remanent polarization, piezoelectric, electrocaloric and pyroelectric responses increase strongly for tensile strains and decrease or vanish for compressive strains.