Ferroelectrics as Smart Mechanical Materials

The mechanical properties of materials are insensitive to space inversion, even when they are crystallographically asymmetric. In practice, this means that turning a piezoelectric crystal upside down or switching the polarization of a ferroelectric should not change its mechanical response. Strain gradients, however, introduce an additional source of asymmetry that has mechanical consequences. Using nanoindentation and contact-resonance force microscopy, this study demonstrates that the mechanical response to indentation of a uniaxial ferroelectric (LiNbO₃) does change when its polarity is switched, and use this mechanical asymmetry both to quantify its flexoelectricity and to mechanically read the sign of its ferroelectric domains.

Ferroelectrics are smart functional materials. Their polarization responds to external stimuli (stress, voltage, and temperature) for transductors and can be switched for memories. Here, we show that, thanks to flexoelectricity, their mechanical response to indentation is also switchable, so that they may be regarded as mechanically smart. A practical consequence, demonstrated here, is the mechanical reading of ferroelectric polarity.

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