Effect of Li/Nb Ratio on the SAW Velocity of 128°Y–X LiNbO3 Wafers

The effects of the composition on the SAW velocity and the electro-mechanical coupling constant (k2) of 128°-rotated Y-cut X-propagating (128°Y–X) LiNbO3 wafers have been quantitatively investigated. The composition of the wafer was determined from the Curie temperature detected by DTA measurements and the SAW velocity from the measurements on a 70 MHz band SAW Comb filter. From the experiments, both the SAW velocity and the k2 obviously depended on the composition of the wafer. Variations of the SAW velocity and the k2 per 1 Li2O mol% were 43.4 m/sec and 0.43%. At the composition of 48.6 Li2O mol% which was reported as the congruent melt composition by Carruthers et al.,1) the SAW velocity and the k2 were 3986 m/sec and 5.8%, respectively.