Giant photostriction in lead-free ferroelectric stemming from photo-excited thermalized carriers

TL;DR

This paper reports the largest observed photoinduced deformation in a ferroelectric thin film, reaching 1%, likely caused by thermalized photoinduced carriers, highlighting a significant advance in photostrictive materials.

Contribution

It demonstrates giant photostriction in a lead-free ferroelectric thin film driven by thermalized carriers, clarifying the microscopic origin of photoinduced deformation.

Findings

Achieved 1% deformation under light illumination.

Identified thermalized carriers as the main cause of photostriction.

Provided insights into microscopic mechanisms of photoinduced deformation.

Abstract

Ferroelectrics are polar materials whose polarization can be switched by applying electric fields; they offer unique opportunities to develop performant photostrictive materials, i.e., materials that can deform under visible light illumination. Naturally devoid of inversion symmetry, they exhibit original photogalvanic effects such as the Bulk Photovoltaic Effect, which relies on ``hot'' photoexcited carriers. It has long been thought that the electric field generated by this effect may couple to the natural piezoelectric abilities of ferroelectrics to provide large photoinduced deformations. However, due to competing effects, such as thermal dilatation, deformation potential, polarization, or depolarizing-field screening by \textit{thermalized} carriers, it remains unclear which microscopic phenomena govern the photoinduced deformations in classical ferroelectric materials. Here, we demonstrate the largest photoinduced deformation measured in a ferroelectric thin film. Reaching 1 %, this giant photostriction likely originates from the contribution of thermalized photoinduced carriers.