On the possibility of existence of a new type of interface acoustic waves at 180° ferroelectric domain boundary

The possibility of existence of a new type of interface acoustic waves (IAW) at 180° ferroelectric domain boundary in single-crystal barium titanate is predicted. Contrary to the known shear-horizontal (SH) interface acoustic wave at such a boundary, the predicted wave for crystallographic propagation direction is polarized in the sagittal plane, that is, the wave is of so-called shear-vertical (SV) polarization, and it has only longitudinal nonzero displacement component at the boundary. The waves become quasi SH-IAW and quasi SV-IAW with a deviation of propagation directions from crystallographic axes. A study of the azimuthal dependence of the wave velocities in the plane of domain boundary shows that quasi SV-IAW exists only in a limited range of the angles (29°-sector) near the direction of spontaneous polarization. In the absence of piezoelectric effect, SV-IAW propagating along crystallographic direction transforms into the interference of two equal-amplitude limiting bulk waves. The feature of this type of wave solution is its existence only under the condition of concavity of slowness surface for quasi-shear bulk waves in sagittal plane. As a result of that a SV-IAW in PZT-4 piezoceramics does not exist