Electroacoustic SAW interaction in strontium titanate

This paper deals with a theoretical investigation into the influence of external electric fields with varying orientation on the velocity of Rayleigh surface acoustic waves (SAW) for (001), (110), and (111) crystallographic planes. The contribution of different nonlinear effects to the SAW velocity variation under the action of external fields is analyzed both for a mechanically squeezed and for a free crystal state. Nonlinear electrostriction has been found to contribute more substantially to the variation of SAW velocity than linear electrostriction. It turns out that because of the linear electrostriction, an external field always provides a greater SAW velocity for all directions of propagation and orientations of saggital plane and the inclusion of nonlinear electrostriction for many propagation directions causes the SAW velocity to decrease. The greatest SAW velocity variation is shown to be 0.016% for the [11~0] propagation direction in the (110) metallized plane at E=20 kV/cm (E/spl par/[110]), i.e., two to three times magnitude less than the appropriate variation of the bulk acoustic wave velocity. Theoretical conclusions are in agreement with experimentally found dependences.