VERIFICATION OF THE NONLINEAR CONSTANTS OF CRYSTALS WITH ILLUSTRATIONS MADE FOR ALPHA-QUARTZ

This article points out weaknesses of several methods used to verify the third-order nonlinear electromechanical constants of crystals. It suggests that the nonlinear constants should be verified by a direct comparison of their values (or the values of their linear combinations) obtained independently from different experiments. This is illustrated by practical examples using the nonlinear constants of quartz. Three fundamental nonlinear constants and twelve linear combinations have been compared; five of them have been found in agreement. Tentative verification criteria for the nonlinear constants have also been formulated.