Giant electromechanical coupling factor of k31 mode and piezoelectric d31 constant in Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 piezoelectric single crystal

High-quality and large piezoelectric single crystals of Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 (PZNT91/09) fabricated by the Bridgman method were investigated regarding the material constants and their temperature dependence. The single crystals poled along [001] of the original cubic direction possess high piezoelectric constants such as g33 and g31 as well as high dielectric constant e33T/e0 (4600), electromechanical coupling factor of the k33 mode (95.3%) and d33 (2500 pC/N). In particular, since k31 and d31 reach 80.8% and -1700 pC/N, respectively, the crystals can be applied for use in sensors and actuators with high performance. Based on the temperature dependence, we inferred that there is a relatively large difference in the elastic compliance (s11E) between rhombohedral and tetragonal phases. The cause of the high piezoelectricity in rhombohedral PZNT91/09 single crystals is thought to be the mechanical softness which leads to easy deformation by the poling field in comparison with the tetragonal phase.