The dependence of k 31 eff on the aspect ratio G = l 1 / l 2 has been calculated for resonators made of ͓001͔ poled 0.67Pb͑Mg 1/3 Nb 2/3 ͒O 3 -0.33PbTiO 3 ͑PMN-0.33PT͒ and ͓011͔ poled 0.71Pb͑Mg 1/3 Nb 2/3 ͒O 3 -0.29PbTiO 3 ͑PMN-0.29PT͒. Based on the derived unified formula, the lateral electromechanical energy conversion efficiency ͉k 31 eff ͉ 2 decreases with G for ͓001͔ poled PMN-0.33PT but increases with G for ͓011͔ poled PMN-0.29PT.

Dispersion relations of Lamb waves and shear horizontal (SH) waves propagating in the [100] and [110] directions of 0.67Pb(Mg1∕3Nb2∕3)O3–0.33PbTiO3 piezoelectric single crystal plate poled along [001]c were calculated. Multiple crossings between symmetric and antisymmetric modes appear due to the moderate anisotropy of these crystals. As frequency increases, the velocities for SH wave modes approach 2.88 and 0.88mm∕μs, respectively, for waves propagating along [100] and [110] directions. These limiting velocities are the corresponding shear velocities of bulk crystals.