Electrical Properties of Li+-Doped Potassium Sodium Niobate Coating Prepared by Supersonic Plasma Spraying

Abstract

The current work aims to compare the effects of systematic A-site substitutions on the electrical properties of potassium sodium niobate (KNN)-based coating. The A-site elements were replaced by Li+ to form (K0.4675Na0.4675Li0.065) NbO3 (KNLN). The pure KNN coating and the Li+-doped potassium sodium niobate (KNLN) coating with dense morphology and single perovskite structure were successfully prepared by supersonic plasma spraying, and the phase composition, microscopic morphology and electrical properties of the two coatings were compared and analyzed in detail by XRD, XPS, three-dimensional morphology and SEM on an Agilent 4294A (Santa Clara, CA, USA) and FE-5000 wide-range ferroelectric performance tester. The results show that: as the polarization voltage increases, the pure KNN coating is flatter and fuller, but the leakage current is large. The KNLN coating has a relatively long hysteresis loop and is easily polarized. The domain deflection responds faster to the external electric field, and the resistance of the domain wall motion to the external electric field is small. The dielectric constant of KNLN coating is 375, which is much higher than that of the pure KNN coating with 125, and the dielectric loss is stable at 0.01, which is lower than that of pure KNN coating at 0.1–0.35. This is because Li+ doping has successfully constructed a polycrystalline phase boundary in which O-T phases coexist, and has higher dielectric properties, piezoelectric properties and ferroelectric properties. At the same time, due to the high-temperature acceleration process in supersonic plasma spraying, the violent volatilization of the alkaline elements Li+, Na+ and K+ leads to the presence of oxygen vacancies and part of Nb4+ in the coating, which seriously affects the electrical properties of the coating.