Dense (K, Na)NbO3 ceramics are successfully fabricated via the cold sintering process at 350°C under a uniaxial pressure of 400 MPa for 4 h. Equimolar KOH and NaOH solutions were utilized as a transient alkaline flux. The microstructure and dielectric properties were studied in detail. Scanning electron microscope and the relative densities reveal dense structures of the ceramics. After post‐annealing at 800°C for 1 h, the ceramics show good electrical performance. The relative dielectric permittivity is 829 (at 10 kHz) at room temperature, and the piezoelectric constant (d33) reaches up to 148 pC/N. The cold sintering technique with equimolar KOH and NaOH solutions as a transient alkaline flux endow KNN ceramics with excellent dielectric and piezoelectric properties, showing a potential way to fabricating other KNN‐based ceramics at low temperature.

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.

A noncontact temperature measurement technique based on fluorescence variation was used to depict the temperature‐dependent evolution of phase transition of a ferroelectric material, that is, Nd3+‐doped (K0.5Na0.5)NbO3 ceramics. The slope of the fluorescence intensity curve changes dramatically in the two temperature regions of 450‐475 K and 650‐675 K, which correspond to orthorhombic‐tetragonal and tetragonal‐cubic transitions as confirmed by the temperature dependence of dielectric constant. Furthermore, the small deviations in δTO‐T and δTc indicate the good accuracy of this noncontact method. This work can guide other ergodic ferroelectrics to describe phase experience by the noncontact fluorescence method.