The Piezoelectric Properties of (Na 0.5 K 0.5 )NbO 3 -K 4 CuNb 8 O 23 Ceramics with Various K 4 CuNb 8 O 23 Doping and Sintering Temperatures

Lead-based piezoelectrics, such as Pb(Zr,Ti)O3 (PZT), ceramics have excellent piezoelectric properties and have been applied to many piezoelectric devices, such as actuators, sensors, and transformers [1, 2]. However, these materials may be restricted because of various environmental problems. Therefore, lead-free piezoelectric materials are being extensively investigated as a replacement for PZT-based ceramics. From among several candidates for lead-free piezoelectric materials, alkali niobate-based materials, such as potassium sodium niobate, are well-known harmless materials and are promising candidates for PZT-based alternative materials due to their excellent piezoelectric properties. The NaxK1-xNbO3 system has a perovskite structure in its composition (x < 0.093). Among the alkali niobate compounds, (Na0.5K0.5)NbO3 (NKN) has a high Curie temperature of more than 400°C and excellent piezoelectric properties [3]. In the case of NKN, it is difficult to achieve high density NKN ceramics because of the volatility of the Na2O and K2O components and its high reactivity to moisture, and so the piezoelectric properties are poor. In order to improve the densification and piezoelectric properties of NKN ceramics, many binary systems have been studied, including NKN-(Ba,Sr)TiO3, NKNKTaO3, NKN-LiNbO3, NKN-LiSbO3, and NKN-K5.4Cu1.3Ta10O29 [35]. Although many binary systems have been studied, the NKNK4CuNb8O23 (KCN) binary system has rarely been done [4]. This paper describes the effect of the KCN addition and the sintering temperature on the phase structure and piezoelectric properties of the NKN ceramics. The optimum sintering temperature, density and microstructure of NKN ceramics with KCN have also been evaluated.