Giant electromechanical coupling factor of K-31 mode in Pb(Zn1/3Nb2/3)O-3-PbTiO3 and Pb(Mg1/3Nb2/3)O-3-PbTiO3 single crystals

Giant electromechanical coupling factor of k(31) mode over 86% was found for (100) Pb[(Zn1/3Nb2/3)(0.91)Ti-0.09]O-3 and (110) Pb[(Mg1/3Nb2/3)(0.74)Ti-0.26]O-3 single-crystal plates poled in the [100] and [110] directions, respectively. The P-E hysteresis loops in the single-crystal plates with giant k(31) become asymmetric. Furthermore, the frequency response of impedance in these plates consisted of a single vibration in the length direction. A mechanism to realize giant k(31) can be explained by the relationship between the crystal plane and poling direction. In addition, the existence of giant piezoelectric d(31) constant was proven by the strain measurement as well as by the impedance measurement.