Composition segregation and grain growth in (K_0.5Na_0.5)NbO₃ piezoceramics prepared by two‐step cold sintering process

Abstract

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.