The elastic constants of piezoelectric crystals

Abstract

The values available in the literature for the elastic constants of the piezoelectric crystals Rochelle salt, potassium dihydrogen phosphate, ammonium dihydrogen phosphate, quartz, sodium chlorate and sodium bromate are assembled. The averages and standard deviations of the estimates are calculated, and the variability of the results discussed. The direct extension and lateral contraction stiffnesses of Rochelle salt show great variability which, however, is much reduced when the elastic constants are expressed as compliances. Little, if any, evidence is found of similar behaviour in the other materials. For comparison with the results on piezoelectric crystals, the available determinations on the non-piezoelectric crystals sodium chloride, lithium fluoride and pyrites are also summarized. It is concluded that elastic constants of crystals are seldom known to better than 1%, and in many cases the uncertainty is considerably larger. This variability is probably due to inherent variability in the materials rather than to experimental error or to differences caused by the use of different experimental methods.