(Na<inf>1-x</inf>K<inf>x</inf>)NbO<inf>3</inf> (NKN)-based lead-free ceramics have been extensively investigated for the replacement of Pb(Zr,Ti)O<inf>3</inf> (PZT)-based ceramics because of their high piezoelectric properties. However, the high sintering temperatures of NKN-based ceramics caused Na<inf>2</inf>O evaporation during sintering. Moreover, the Na<inf>2</inf>O evaporation reduced the polling efficiency and changed the microstructure and eventually degraded the piezoelectric properties of the NKN-based ceramics. Therefore, because the Na<inf>2</inf>O evaporation occurred at temperatures above 1,000°C, it is necessary to find a method to reduce the sintering temperature of the NKN-based ceramics to below 1,000°C in order to obtain reliable piezoelectric properties. In general, two methods have been used to reduce the sintering temperature of NKN-based ceramics (1) addition of sintering aids and (2) spark plasma sintering (SPS). In this chapter, detailed discussions about these two methods will be presented.
ASJC Scopus subject areas