# Flexoelectric Polarization Enhancement in Paraelectric BaHfO3 via Strain Gradient Engineering

## TL;DR

This paper shows that strain gradients in BaHfO3 thin films can significantly enhance polarization through flexoelectric effects, even without phase transitions.

## Contribution

Demonstrates a 29-fold polarization enhancement in centrosymmetric BaHfO3 via strain gradient engineering, isolating flexoelectric coupling.

## Key findings

- A strain gradient exceeding 10⁵ m⁻¹ in BaHfO3 thin films leads to a 29-fold increase in field-induced polarization.
- Flexoelectric coupling is confirmed as the source of enhanced polarization in a centrosymmetric paraelectric material.
- The study provides a benchmark for distinguishing flexoelectric effects from ferroelectric and piezoelectric contributions.

## Abstract

Flexoelectricity – polarization induced by strain gradients – offers a route to polar functionality in centrosymmetric dielectrics, where traditional piezoelectric effects are absent. This study investigates the flexoelectric effect in epitaxial BaHfO3 (BHO) thin films, a centrosymmetric and paraelectric perovskite. While a large lattice mismatch induces defect‐driven relaxation, a coherently grown BHO film undergoes elastic relaxation, forming intrinsic strain gradients exceeding 105 m−1. A 29‐fold enhancement in spontaneous polarization is observed at an electric field of 4 MV cm−1 for BHO exhibiting a strain gradient compared to relaxed BHO. This enhancement is attributed to flexoelectric coupling, which is isolated from ferroelectric and piezoelectric contributions due to the centrosymmetric nature and the absence of phase transitions in BHO. The findings establish a clear link between engineered strain gradients and enhanced polarizability in oxide thin films, offering a benchmark system for deconvoluting the flexoelectric effect from other polar effects. These results provide a basis for exploiting flexoelectricity in dielectric devices and advance the fundamental understanding of strain‐coupled phenomena in functional oxides.

A strain gradient exceeding ≈105 m−1 in coherently grown BaHfO3 thin films induces a 29‐fold enhancement in field‐induced polarization. These results demonstrate flexoelectric coupling in a centrosymmetric paraelectric oxide thin film, offering a route to polarization control without relying on ferroic phase transitions.