Elevating electrical properties of (K, Na)NbO₃ceramics via cold sintering process and post‐annealing

Abstract

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.

Composition segregation and grain growth in (K0.5Na0.5)NbO3 piezoceramics prepared by two‐step cold sintering process

“…However, because the high temperature accelerates the transfer rate of alkali metal elements, the ratio of K/Na is changed after CSP. Of course, the density of CSP5 is only 74%, and it has obvious porosity, and there is no K‐rich phase, which cannot effectively suppress the volatilization of alkali metal elements during the annealing process 23,25 …”

“…Using NaCl aqueous solution as a solvent can change the microstructure of KNN ceramics, inhibit the volatilization of alkali metal elements, and reduce the sintering temperature to 900°C 24 . When the solvent is an equimolar KOH and NaOH solution, the sintering temperature was reduced to 800°C after a 350°C CSP 25 . In the reported studies, CSP can reduce the preparation temperature of KNN ceramics to below 900°C.…”

“…23 Using NaCl aqueous solution as a solvent can change the microstructure of KNN ceramics, inhibit the volatilization of alkali metal elements, and reduce the sintering temperature to 900 • C. 24 When the solvent is an equimolar KOH and NaOH solution, the sintering temperature was reduced to 800 • C after a 350 • C CSP. 25 In the reported studies, CSP can reduce the preparation temperature of KNN ceramics to below 900 • C. This method effectively reduces the volatilization of K/Na elements while maintaining the high performance of KNN ceramics. Therefore, the preparation of KNN ceramics by CSP shows the obvious advantages and it is quite significant to further investigate it.…”

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

“…In this work, the Mn‐doped KNN‐based ceramics were successfully prepared through cold sintering and post‐sintering via selecting KMnO 4 solution as a transient solution. The extra K in solution can further compensate the high‐temperature K volatilization and reduce its negative effect on piezoelectric property for KNN ceramics, as our previous work reported 24,26 . The new doping strategy of CSP has been explored in detail, and the effect of Mn on the electrical properties of KNN ceramics has been studied.…”

“…The extra K in solution can further compensate the high-temperature K volatilization and reduce its negative effect on piezoelectric property for KNN ceramics, as our previous work reported. 24,26 The new doping strategy of CSP has been explored in detail, and the effect of Mn on the electrical properties of KNN ceramics has been studied. With respect to Mn-doped KNN ceramics prepared by conventional sintering (CS), the higher density, larger grain size, and higher piezoelectric property were obtained in the ceramics prepared via cold sintering methods.…”