The anomalous elastic anisotropy of Li2B4O 7 and its influence on SAW properties

The anomalous elastic anisotropy of Li₂B₄O ₇ caused by the “incorrect” relation between two elastic moduli, c₃₃ and c₄₄, 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 (φ,θ,90), where φ is arbitrary when θ=40...46°. If φ=45° the permitted interval of θ angle is the largest: θ=35-68