Influence of MnO_2 Doping on the Dielectric and Piezoelectric Properties and the Domain Structure in (K_(0.5)Na_(0.5))NbO_3 Single Crystals

摘要

MnO_2-doped (K_(0.5)Na_(0.5))NbO_3 (KNN) single crystals were grown by high-temperature solution method using K_2CO_3-Na_2CO_3 eutectic composition as flux. The effect of the manganese dopant on the dielectric, piezoelectric properties and the domain structure was investigated. The Mn02-doped KNN crystals were found to exhibit higher piezoelectric coefficient d_(33) and dielectric permittivity ε_r when compared with pure KNN crystal, being on the order of 270 pC/N and 730, respectively, for manganese-doped level at 0.5 mol%, with slightly reduced orthorhombic to tetragonal phase transition T_(o-t), and Curie temperature T_C, being on the order of 193° and 416℃, respectively. The domain size of [001)-oriented KNN-Mn crystal was found to be on the order of 5-13 μm at room temperature, smaller than that of the domain size observed in the pure KNN crystal (20-30 μm). The thermal depoling experiments were performed on the [001]-poled KNN-Mn crystals, where the partial depolarization was found to occur at temperatures above 200℃, due to the phase transformation.