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

MnO 2 ‐doped (K 0.5 Na 0.5 )NbO 3 (KNN) single crystals were grown by high‐temperature solution method using K 2 CO 3 –Na 2 CO 3 eutectic composition as flux. The effect of the manganese dopant on the dielectric, piezoelectric properties and the domain structure was investigated. The MnO 2 ‐doped KNN crystals were found to exhibit higher piezoelectric coefficient d 33 and dielectric permittivity ɛ 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°C, 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°C, due to the phase transformation.