Through mixing the KMnO4 solution with K0.5Na0.5NbO3 (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.

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In this work, the effects of Sb doping on the electrical conductivity of fine-grain 0.9(K0.5Na0.5)(Nb1−xSbx)O3-0.1Bi(Ni2/3Nb1/3)O3 (KNNSx-BNN) ceramics were systemically investigated. It was found that the grain size decreases from ~900 nm (x = 0) to ~340–400 nm (x = 0.06–0.08), and then increases again to ~700 nm (x = 0.10). This is because the solubility limit of Sb doping is about 0.08 in this ceramic, and more Sb doping will facilitate the grain growth as the sintering aids. Impedance and conductivity analyses reveal that the grain resistance and its activation energy show a similar changing tendency with grain size, while grain boundary conductivity steadily increases after Sb doping. In this process, the grain contribution on ceramic conductivity changes with grain size variation, and grain boundary contribution becomes more obvious with increasing doping content. The reduction in grain size, improvement in grain boundary density and doping ions entering into the grain boundary should contribute to the evolution of electrical conductivity properties after Sb doping in KNN-based ferroelectric ceramics.

Cold sintering process (CSP) is a new method to prepare ceramics under quite low temperature. In this work, two‐step CSP under different pressures was employed to prepare (K0.5Na0.5)NbO3 (KNN) ceramics. The density of KNN green pellets can be raised by enhancing the pressure of second‐step CSP. Energy‐dispersive spectroscopy reveals the composition segregation of A‐site cations in large grains. The dissolution rate of K+ in an aqueous medium is faster than Na+, and high pressure can accelerate K+ dissolution, resulting in more Na+ in some grains. Besides, the diffusion rate of Na+ in grains is better than K+, which promote the grains growth. Finally, the piezoelectric property is improved even with low ceramic density due to the larger grains, which possess the higher performance composition. This result demonstrates that the pressure and inhomogeneous dissolution of alkali metal ions among CSP play an important role in grain growth and piezoelectric enhancement.