New solutions of shear waves in piezoelectric cubic crystals

Acoustic wave propagation in piezoelectric crystals of classes 4 3m and 23 is studied. The crystals Tl3VS4 and Tl3TaSe4 ( 4 3m) of the Chalcogenide family and the crystal Bi12TiO20 (23) possess strong piezoelectric effect. Because the surface Bleustein-Gulyaev waves cannot exist in piezoelectric cubic crystals, it was concluded that new solutions for shear-horizontal surface acoustic waves (SH-SAWs) are found in the monocrystals using different electrical boundary conditions such as electrically “short” and “open” free-surfaces for the unique [101] direction of wave propagation. For the crystal Tl3TaSe4 with coefficient of electromechanical coupling (CEMC) K e 2 =e 2/(C×g)∼1/3, the phase velocity V ph for the new SH-SAWs can be calculated with the following formula: V ph=(V a+V t)/2, where V t is the speed of bulk SH-wave, V t=V t4(1+K e 2 )1/2, V a=a K V t4, a K=2[K te(1+K e 2 )1/2−K e 2 ]1/2, and V t4=(C 44/ρ)1/2. It was found that the CEMC K 2 evaluation for Tl3TaSe4 gave the value of K 2=2(V f−V m)/V f∼0.047 (∼4.7%), where V f∼848 m/s and V m∼828 m/s are the new-SAW velocities for the free and metallized surfaces, respectively. This high value of K 2(Tl3TaSe4) is significantly greater than K 2(Tl3VS4)∼3% and about five times that of K 2(Bi12TiO20).