Piezoelectric properties of tetragonal K _0.95Li _0.05Ta _x Nb _1-xO ₃ lead-free single crystals near tetragonal-cubic phase transition boundary

Tetragonal K _0.95Li _0.05Ta _x Nb _1-x O ₃ lead-free single crystals have been grown by top-seeded solution growth technique. Dielectric and piezoelectric properties of poled samples were investigated as a function of temperature and dc bias. Both orthorhombic- tetragonal and tetragonal-cubic phase transition temperatures shift to lower temperatures as the Ta content increased. High piezoelectric activity was found to the crystal near the tetragonal-cubic phase transition boundary, which is due to phase transition as well as domain instability. For K _0.95Li _0.05Ta _0.59Nb _0.41O3 single crystal, piezoelectric coefficient (d ₃₁) and electromechanical coupling factor (k ₃₁) achieved -340pCN ^-1 and -40%, respectively, which were much larger than those of lead-based Pb(Zr,Ti)O ₃.