Longitudinal piezoelectricity in natural calcite materials: Preliminary studies

Here we report a preliminary quantitative investigation into calcite piezoelectricity using a combination of quantum mechanical modelling and electromechanical characterisation of naturally occurring calcite crystals and structures. The low symmetry of crystallised biomolecules - from amino acids and peptides to viruses and fibrous proteins - can result in useful electrical properties, including ferroelectricity, pyroelectricity, and piezoelectricity. Biominerals such as hydroxyapatite and calcite are generally not considered piezoelectric. This data represents the first quasi-static, longitudinal piezoelectric measurements on macroscopic calcite based materials; namely Icelandic spar and a variety of beach specimens. We substantiate these measurements using Density Functional Theory (DFT) calculations, which attribute the measured weak, residual piezoelectric response in all directions to centrosymmetric calcite crystals. Our data is consistent with the observation of second harmonics generation by calcite microcrystals occurring in the human pineal gland.