Dielectric and piezoelectric properties of lead-free (K0.44Na0.46)NbO3-0.5%MnO2 single crystals grown by the TSSG method

Lead-free (K0.44Na0.46)NbO3-0.5%MnO2 (KNN-0.5%MnO2) single crystals with dimensions of Ф30×10 mm were successfully grown by a top seeded solution growth technique (TSSG). The X-ray diffraction pattern has shown that the as-grown crystals have an orthorhombic perovskite structure. The orthorhombic-tetragonal (TO-T) and tetragonal-cubic phase transition temperature (the Curie temperature TC) of the single crystal were found at 184 °C and 412 °C, respectively. The KNN-0.5%MnO2 single crystals exhibited high piezoelectric constants d33 and dielectric permittivity εr, being 261 pC/N and 275. Well saturated P-E hysteresis loop with remnant polarization Pr=22.06 µC/cm2 and coercive field Ec=17.93 kV/cm was obtained at a maximum electric field of 3 kV/mm. A high strain (0.24%) and electromechanical coupling coefficient Kt (65.9%) were obtained along the (001) orientation. These excellent results indicated that the KNN-0.5%MnO2 single crystals could be used as high quality lead-free material.