The origins of electromechanical indentation size effect in ferroelectrics

TL;DR

This paper investigates the size-dependent electromechanical behavior of ferroelectrics, demonstrating an electromechanical size-effect in BaTiO3 and attributing it to flexoelectricity rather than dislocation activity.

Contribution

It provides experimental evidence of size effects in ferroelectrics and identifies flexoelectricity as the key mechanism, contrasting with mechanisms in metals.

Findings

Size-dependent electromechanical behavior observed in BaTiO3

Flexoelectricity identified as the primary mechanism

Contrast with non-ferroelectric piezoelectric Quartz

Abstract

Metals exhibit a size-dependent hardening when subject to indentation. Mechanisms for this phenomenon have been intensely researched in recent times. Does such a size-effect also exist in the electromechanical behavior of ferroelectrics?--if yes, what are the operative mechanisms? Our experiments on BaTiO3 indeed suggest an electromechanical size-effect. We argue, through theoretical calculations and differential experiments on another non-ferroelectric piezoelectric (Quartz), that the phenomenon of flexoelectricity(as opposed to dislocation activity) is responsible for our observations. Flexoelectricity is the coupling of strain gradients to polarization and exists in both ordinary and piezoelectric dielectrics. In particular, ferroelectrics exhibit an unusually large flexoelectric response.