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Abstract: Acoustic wave propagation in piezoelectric crystals of classes 4̄3m and 23 is studied. The crystals Tl₃VS₄ and Tl₃TaSe₄ (4̄3m) 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_e²=e²/(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_e²)^1/2, V_a=a_KV_t4, a_K=2[K_e(1+K_e²)^1/2−K_e²]^1/2, and V_t4=(C₄₄/ρ)^1/2. It was found that the CEMC K² evaluation for Tl₃TaSe₄ gave the value of K²=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 K²(Tl₃TaSe₄) is significantly greater than K²(Tl₃VS₄)~3% and about five times that of K²(Bi₁₂TiO₂₀).

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