Microstructure and electrical property of NaNbO3 ceramics prepared by cold sintering process assisted post-heat-treatment

Highlights: • Cold sintering process (CSP) at 120 °C could significantly improve the initial relative density of NaNbO₃ (NN) ceramics up to 92.6%, but has no effect on the phase structure. • A subsequent post-heat-treatment (PHT) at 1230 °C after CSP could significantly improve the relative density to 96.9% and keep a small average grain size around 3.65 μm. • The NN ceramics prepared by CSP-PHT demonstrated larger polarization of 34.2μC/cm², much larger than those prepared by conventional sintering method at 1300 °C with polarization of 24.8μC/cm². -- Abstract: NaNbO₃ (NN) ceramics have attracted worldwide attention as a kind of dielectric material, but with the drawbacks of difficulty in sintering. In this work, high performance NN ceramics were achieved by using cold sintering process assisted post-heat-treatment (CSP-PHT). The effects of cold sintering process (CSP) and post-heat-treatment (PHT) of NN ceramics on the microstructure and electrical properties were systematically investigated. High dense NN ceramics with relative density of 92.6% were achieved by CSP, which increased to 96.9% with improved crystallinity after PHT at 1230 °C. Of particular interest is that the NN ceramics prepared by CSP-PHT exhibited typical ferroelectric hysteresis loops with large polarization of 34.2 μC/cm², which is much higher than the conventional sintering (CS) method at 1300 °C with value of 24.8 μC/cm². Our work shows that CSP-PHT is an effective method to obtain high-performance NN ceramics at lower sintering temperature.