From Solid to Liquid Piezoelectric Materials

Abstract

The history and evolution of the piezoelectricity isreviewed starting from the discovery of pressure (“piezo” in Greek) electricity by the Curie Brothers in a ferroelectric crystal, up today when liquid piezoelectricity was observed in polar anisotropic fluids, the ferroelectric nematic liquid crystal (NF) materials. As effects analogous to the piezoelectricity have been observed in various crystals, polymers and biomaterials with lack of inversion symmetry, so the definition of the piezoelectricity has been evolved to describe a linear coupling between mechanical stress and electric polarization. A mechanical stress induced electric polarization is called direct piezoelectricity, and an electric field induced mechanical stress is called converse piezoelectricity. Soon after the discovery of ferroelectricity in chiral liquid crystals with two- and one-dimensional fluid order, owing to the lack of their inversion symmetry, linear electromechanical effects analogous to the direct and converse piezoelectricity have also been observed in those materials. While thesematerials in certain directions can sustain static stress, the NF phase is truly three-dimensional fluid, and a steady stress can only be sustained by surface tension. The review is concluded by a summary and analysis of direct and converse piezoelectric measurements on several NF materials, and by recapping the challenges and possible future applications of liquid piezoelectricity.