Control of piezoelectricity in amino acids by supramolecular packing

Piezoelectricity, the linear relationship between stress and induced electrical charge, has attracted recent interest due to its manifestation in biological molecules such as synthetic polypeptides or amino acid crystals, including gamma (gamma) glycine. It has also been demonstrated in bone, collagen, elastin and the synthetic bone mineral hydroxyapatite. Piezoelectric coeffcients exhibited by these biological materials are generally low, typically in the range of 0.1-10 pmV(-1), limiting technological applications. Guided by quantum mechanical calculations we have measured a high shear piezoelectricity (178 pmV(-1)) in the amino acid crystal beta (beta) glycine, which is of similar magnitude to barium titanate or lead zirconate titanate. Our calculations show that the high piezoelectric coeffcients originate from an effcient packing of the molecules along certain crystallographic planes and directions. The highest predicted piezoelectric voltage constant for beta-glycine crystals is 8VmN(-1), which is an order of magnitude larger than the voltage generated by any currently used ceramic or polymer.