K 0.5 Na 0.5 NbO 3 ceramics fabricated by combining cold sintering with annealing in air atmosphere or low pO 2 atmosphere

• Published in: Journal of the American Ceramic Society 2023-11, Vol.106 (11), p.6826-6836
• Main Authors: Lan, Jia‐jun, Chen, Xiao‐ming, Liu, Mei‐dan, Liu, Li‐na, Lian, Han‐li
• Format: Article
• Language: English
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/jace.19316

Dense K 0.5 Na 0.5 NbO 3 lead‐free ceramics were successfully fabricated by combining cold sintering process (CSP) with annealing in air atmosphere or low pO 2 atmosphere. Acetic acid was used as transition liquid. By optimizing the liquid content and pressure during CSP, the CSP samples with relative densities 74.2% were obtained with adding 15 wt% acetic acid under 800 MPa. The CSP samples were then annealed in air atmosphere between 1000 and 1100°C. The ceramics annealed at 1050°C exhibit excellent electrical properties with piezoelectric constant d 33  = 125 pC/N, dielectric constant ε r  = 509, dielectric loss tan  δ  = 0.04, and remanent polarization P r  = 38.17 μC/cm 2 . Additionally, the mixture of K 0.5 Na 0.5 NbO 3 and base metal Ni powders was also cold‐sintered and then annealed in the low pO 2 atmospheres in order to detect whether Ni was oxidized or not. The optimized low pO 2 atmospheres to protect the Ni from oxidation are pO 2  = 10 −10  atm followed by reoxidizing in pO 2  = 10 −6  atm. The K 0.5 Na 0.5 NbO 3 fabricated by CSP with annealing in the optimized low pO 2 atmospheres exhibits comparable electrical properties of the ceramics annealed in air atmosphere, providing an optional approach for using base metals as electrodes.