Enhanced piezoelectric property in Mn-doped K0.5Na0.5NbO3 ceramics via cold sintering process and KMnO4 solution

Through mixing the KMnO₄ solution with K_0.5Na_0.5NbO₃ (KNN) powders, cold sintering process (CSP) was employed to fabricate high-density Mn-doped KNN green pellets and ceramics. The microstructure, doping effect of Mn and electrical properties of these ceramics were studied in detail. Compared with conventional sintering (CS), the CSP supports the homogeneity of dopants and then promotes grain growth and ceramic densification; thus the Mn-doped KNN ceramics prepared by CSP show the obviously higher density and larger grain size. Besides, the less alkalis volatilization and oxygen vacancies result in more Mn³⁺ but less Mn⁴⁺ in CSP ceramics compared to CS ones, which endows the pinning effect and good poling characteristics in CSP ceramics. All the previous results contribute to the high dielectric constant and remnant polarization in CSP ceramics, which support the enhanced piezoelectric coefficient and are much superior than Mn-doped KNN ceramics prepared by CS. This work reveals that CSP can be a new doping strategy to perform chemical modification of electrical properties in KNN ceramics.