Cold sintering of the ceramic potassium sodium niobate, (K0.5Na0.5)NbO3, and influences on piezoelectric properties. Issue 1 (January 2022)

• Record Type: Journal Article
• Authors: Tsuji, Kosuke; Fan, Zhongming; Bang, Sun Hwi; Dursun, Sinan; Trolier-McKinstry, Susan; Randall, Clive A.
• Is Part Of: Journal of the European Ceramic Society. Volume 42:Issue 1(2022)
• Page Start: 105
• Page End: 111
• Publication Date: 2022-01
• Subjects: Cold sintering process -- Potassium-sodium niobate -- Piezoelectric ceramics -- Lead-Free piezoelectrics -- Low temperature sintering; Ceramic materials -- Periodicals; Composite materials -- Periodicals; Matériaux céramiques -- Périodiques; Composites -- Périodiques; Ceramic materials; Composite materials; Periodicals; Electronic journals; 666.05
• DOI: 10.1016/j.jeurceramsoc.2021.10.002
• Languages: English
• ISSNs: 0955-2219

Abstract

Abstract: Cold Sintering was applied to densify a Potassium-Sodium Niobate solid solution composition, 0.5KNbO3 -0.5NaNbO3 (KNN); the process uses a transient chemical sintering aid, moderate pressure (400 MPa), and temperatures between 230–300 °C to obtain ceramics of ∼92 to 96 % theoretical density. Typically, sintering temperatures between ∼1000−1050 °C are required to density KNN using conventional methods. In this paper, the densification was investigated during heating, particularly the shrinkage in the first 60 min of the cold sintering process. The low-field dielectric and electrical properties of the resulting ceramics were found to be comparable to conventionally sintered KNN. Electric fields up to 80 kV/cm could be applied, however the ceramics showed pinched hysteresis loops, even after poling over a wide range of temperatures and electric fields. A Rayleigh analysis was used to investigate domain dynamics and high reversible permittivity. The irreversible behavior was an order of magnitude lower than in conventionally sintered KNN, likely associated with defect pinning of ferroelectric domains. A Transmission Electron Microscopy (TEM) study revealed a high density of line defects in most grains; dislocations in the grains limit poling and domain wall movement, thus suppressing both the piezoelectric properties and the hysteresis. Furthermore, TEM observations indicated crystalline grain boundaries that were faceted with terrace kink ledges. These observations point to the importance of the initial powder optimization and grain boundary diffusion when using cold sintering to prepare ceramics that are intended to show bulk cooperative properties such as ferroelectricity. The impact of limited high temperature homogenization of bulk diffusional processes is discussed.