Sectors of nonexistence of surface acoustic waves in potassium niobate

Large sectors of azimuthal directions (up to 17.6°) are numerically revealed for the free surface of potassium niobate where normal (that is, nonleaky) surface acoustic waves (SAWS) could not be propagated. The computed maps of such sectors show the cases when a common definition of effective electromechanical coupling coefficient for SAWS, Δν/ν, is invalid and should be revisited. In contrast to previous studies.. the true regions of the existence of pure shear Bleustein-Gulyaev (BG) waves on the free surface of the rotated cuts of potassium niobate are found to be very small and are restricted to the orientations very close to the X- and Y-cuts. In the intermediate range of rotated cuts, BG waves transform into an unphysical solution rather than leaky waves that prevents the estimation of electromechanical coupling factor using the Δν/ν definition. Applicability of the method of first integrals to derive an explicit secular equation for BG waves on the rotated cuts of piezoelectric crystals is demonstrated. This equation, as found, is bicubic. A comparison of analytical and numerical results is still in progress.