Abstract
In lattices in which not all ions possess inversion symmetry, internal-strain effects give rise to piezoelectricity and contribute to the elastic response. It is possible to describe these internal strains as static optical-phonon-mode displacements and to analyze the internal-strain contributions to the elastic and piezoelectric constants accordingly. Certain symmetry properties become evident as a result, the most general of which is that only Raman-active modes contribute to internal strain, and only modes simultaneously Raman- and infrared-active produce piezoelectricity. This formalism also provides a basis for a discussion of piezoelectric and elastic anomalies which may accompany incipient instabilities in opticalphonon modes. Finally, it is shown that the anomalous elastic behavior of quartz near the transition temperature can be understood by postulating a low-frequency temperature-dependent Raman-active mode of symmetry.
- Received 6 June 1967
DOI:https://doi.org/10.1103/PhysRev.163.924
©1967 American Physical Society