Piezo and pyroelectricity in electrets : caused by charges, dipoles, or both?
Gerhard Martin Sessler, Dilip K. Das‐Gupta, Aime S. DeReggi, Wolfgang Eisenmenger, T. Furukawa, José Alberto Giacometti, Reimund Gerhard · OPUS Publication Server of the University of Stuttgart (University of Stuttgart) · 1992
In a homogeneous medium space charges cannot cause piezo or pyroeiectricity. If stressed, there will be affine geometrical changes throughout the medium, and therefore the induction charges on the electrodes will remain the same, and piezoelectricity cannot be generated. However, if dipoles are present in such a homogeneous dielectric, then piezoelectricity is possible. In an inhomogeneous medium such as a semicrystalline polymer, charges and dipoles can cause piezoelectricity. If you have, for instance, a semicrystalline polymer then the crystalline and the amorphous parts are, upon compression, subjected to different degrees of deformation; and for this reason, a piezoelectric effect can be generated.