The anomalous elastic anisotropy of Li/sub 2/B/sub 4/O/sub 7/ and its influence on SAW properties

The anomalous elastic anisotropy of Li/sub 2/B/sub 4/O/sub 7/ caused by the "incorrect" relation between two elastic moduli, c/sub 33/ and c/sub 44/, is proved to be responsible for the existence of earlier found undamped longitudinal horizontally polarized (LH) type leaky waves. A simple proof is presented to show that "ray-polarized" quasilongitudinal bulk wave propagating in the plane of reflectional symmetry satisfies the stress-free conditions when the boundary plane is parallel to polarization vector and orthogonal to the plane of reflectional symmetry. The close relation between the particular directions, such as acoustic axes, and the existence of "non-leaky" waves is analyzed using the "exceptional wave line" method. LH type leaky waves exist in crystal cuts with Euler angles (/spl phi/,/spl theta/,90), where /spl phi/ is arbitrary when /spl theta/=40...46/spl deg/. If /spl phi/=45/spl deg/ the permitted interval of /spl theta/ angle is the largest: /spl theta/=35-68.