External homogeneous electric field effect on the properties of Rayleigh SAW in lithium niobate

The effect of differently oriented external electric fields on the velocity of Rayleigh surface acoustic wave (SAW) in LiNbO/sub 3/ is theoretically studied for crystallographic XY, YZ, XZ planes for both mechanically squeezed and mechanically free crystal states. Even and odd portions of velocity variation versus the applied external electric field have been computed. The odd portion was revealed to be negative in all situations, metallized or not, except the XY plane for the mechanically free crystal with the electric field orientation normal to its surface. It is shown that the mechanical state of a crystal substantially affects electroacoustic interaction by varying its anisotropy and intensity. The SAW velocity alteration is always greater for the mechanically free crystal than for the squeezed one. The surface metallization leaves the anisotropy and velocity variations essentially unchanged, except for the case of the XY plane and the normal field orientation. As stated, metallized surfaces promote both slower and faster SAW velocities. The maximum variation of the even and odd portions of the SAW velocity dependence on the external electric field constitute 0.005% and 0.2%, respectively, in the YZ and XZ planes at E=100 kV/cm. The results obtained correlate well with experimental data.