Origin of Piezoelectricity in an α-Quartz

The piezoelectric effect in an α-quartz crystal (low temperature phase) is discussed by using a rigid stick-bar model. At the transition from a β-(high temperature phase) to α-quartz, the unit tetrahedrons (SiO4) rotate alternately around its electric X axis, although in a β-quartz crystal the unit tetrahedrons are arranged helically along the optic Z axis. X-ray data of an α-quartz reveal small contractions along the X and Y axes. As a result of the contractions, distortion of the unit tetrahedron causes an electric polarization along the electric axis in the unit inducing the piezoelectric effect in the quartz crystal.