Elastic constants of langasite and alpha quartz at high temperatures measured by antenna transmission acoustic resonance.

A method for measuring elastic constants of piezoelectric materials at high temperature up to 1224 K is proposed. It determines all independent elastic constants by measuring resonance frequencies of a rectangular parallelepiped piezoelectric specimen contactlessly using its own piezoelectricity with an antenna. Without using conventional contacting piezoelectric transducers, vibrational sources are excited directly in the specimen by the oscillating electric field. Capability of the method is demonstrated by measuring the elastic constants of langasite at high temperature up to 1224 K, and temperature coefficients of the elastic constants are determined. In addition, elastic constants of alpha quartz are measured at high temperature up to just below the alpha-beta phase transition temperature. Considering the local deformation with temperature increment, an interpretation based on the strain energy reduction is proposed for the unusual temperature dependence of C(66). Furthermore, the internal-friction tensor is measured, and the relationship between the observed anisotropy in internal friction and the structural evolution with temperature increment is discussed.