The elastic, piezoelectric, and dielectric constants, and their temperature dependence within the range 0°–110°C, have been determined for single crystals of lithium tantalate and lithium niobate. For each material, the constants were extracted from a combination of many ultrasonic phase-velocity measurements, the measured resonant and antiresonant frequencies of a single length-extensional bar resonator, and the measured low-frequency capacitances of two thin flat-plate specimens. For lithium tantalate, the normalized first temperature derivatives of the elastic constants range from −0.4 to −6.7×10−4/°C, while the derivatives for the piezoelectric stress constants range from −1.3 to +1.5×10−4/°C. In the case of lithium niobate, the elastic constant temperature derivatives are all on the order of −2×10−4/°C, while the piezoelectric temperature derivatives are all positive in the range 0.8–8.9×10−4/°C. The dielectric or permittivity temperature derivatives are positive for both materials.

The principal thermal expansion coefficients of single crystals of LiTaO3, LiNbO3 and α quartz (for reference purposes) have been determined by an x-ray diffraction technique in the temperature range 25°–500°C. All three materials crystallize in the trigonal system, the first two in class 3m and the last one in class 32, and are characterized by only two principal expansion coefficients, parallel and normal to the c or Z axis. The Bragg x-ray angle data were fitted to suitable polynomials in the temperature deviations from an arbitrary reference of 25°C, and the expansion coefficients up to second order calculated from the coefficients of these polynomials. The Z-axis expansion of LiTaO3 showed a definite maximum at about 250°C. Similar behavior was indicated in the Z-axis expansion of LiNbO3, but at a much higher temperature (at the high extreme of the measurement range). The expansion of all three crystals normal to the Z axis was quite regular.

The third-order elastic moduli of several isotropic polycrystalline metals have been determined from measurements of the velocities of both longitudinal and shear ultrasonic waves in uniaxially stressed specimens. In each case, the wave-propagation direction was chosen normal to the applied stress, and the shear waves were polarized either normal or parallel to the stress direction. Hence, a unique evaluation of all three thirdorder moduli was possible using the recent theory of Thurston and Brugger, specialized for isotropic symmetry. The measuring equipment is based on a new variation of the pulse-echo interferometric technique and is capable of resolving velocity changes of a few parts in 106. Results are presented for several steels, aluminum alloys, magnesium, tungsten, and molybdenum, and are shown to be in good agreement with alternative nonlinear elasticity data, including static measurement of the pressure derivatives of the bulk and shear moduli.

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Room-temperature values for all six independent elastic coefficients (at constant electric field) and all four independent piezoelectric stress coefficients have been determined from ultrasonic velocity measurements on a single-crystal specimen of lithium tantalate grown by the Czochralski technique. The two independent dielectric constants at constant strain were derived from low-frequency measurements on thin plates of lithium tantalate, in conjunction with the relevant elastic and piezoelectric data. The numerical results have been used to map the deviation of the elastic energy flux vector from the wave propagation direction for plane elastic wave propagation in the YZ crystallographic plane.