| The ultrasonic harmonic generation technique previously used to measure third-order elastic (TOE) constants of crystals of cubic symmetry has been extended to measurement of crystals of trigonal symmetry. The theory for nonpiezoelectric trigonal crystals of J. Philip {lcub}Technical Report No. 22, Office of Naval Research, Contract No. N00014-81-K-0229 (to be published in 1983){rcub} has been combined with the piezoelectric theory of McMahon {lcub}J. Acoust. Soc. Am. 44, 1007 (1968){rcub} to determine the effective TOE constants in a piezoelectric solid, and correction has been made in McMahon's expression.; Measurements in weakly piezoelectric quartz have produced values of C(,111) and C(,333) which agree within experimental uncertainty with values of R. N. Thurston, H. J. McSkimin and P. Andreatch, Jr. {lcub}J. Appl. Phys. 37, 267 (1966){rcub} and R. Stern and R. T. Smith {lcub}J. Acoust. Soc. Am. 44, 640 (1968){rcub} after corrections have been made for the effect of diffraction on the data. Measurements in strongly piezoelectric LiNbO(,3) have resulted in values which agree reasonably well with those of J. Philip and M. A. Breazeale {lcub}Proc. IEEE Ultrasonics Symposium, Vol. 2 (1982){rcub} but disagree with those of C. Y. Nakagawa, K. Yamanouchi and K. Shibayama {lcub}J. Appl. Phys. 44, 3969 (1973){rcub}. There is indication of some sample dependence of the values of both the second-order elastic constants as well as the third-order elastic constants of LiNbO(,3) samples currently available.; In the course of measurement of the TOE constants a negative nonlinearity parameter was observed for the Piezoelectric {lcub}100{rcub} direction in quartz. This peculiarity is impossible for thermodynamic reasons in fluids, but has been observed once previously in fused silica {lcub}J. Bains and M. A. Breazeale, J. Acoust, Soc. Am. 57, 745 (1975){rcub}. The nonlinearity parameter appears to be positive for the piezoelectric {lcub}001{rcub} direction in LiNbO(,3).; The data presented are for the "piezoelectrically stiffened" TOE constants; however, there are preliminary indications that the harmonic generation technique may give access to the constant field TOE constants; (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI)... |
