Preparation And Piezoelectric Properties Of K_0.5NA_0.5NBO₃-Based Lead-Free Piezoelectric Ceramics

For environmental protection reasons, potassium sodium niobate ((K0.5NA0.5)NbO3)-based ceramics have been considered as promising alternatives to lead-based materials which are currently used in majority of ultrasonic applications. However, it is very difficult to process the ceramics to full density by ordinary sintering under atmospheric conditions, which deteriorates their properties and restricts their uses in industrial productions. In this chapter, the preparation of KNN-based ceramics with well-densified structure, good piezoelectric and dielectric properties are reported. Novel sintering aids CuO and MnO are used to improve the densification and hence the electrical properties of the ceramics. The additional hardening effects of the sintering aids are also discussed. The piezoelectric properties of the ceramics are further enhanced via the formation of new solid solutions with other ferroelectrics, such as LiSbO3, LiTaO3, BaTiO3and Ba(Zr0.05Ti0.95)O3. After the formation of new solid solutions, the ferroelectric tetragonal-ferroelectric orthorhombic phase transition is shifted to lower temperatures, such that the ceramics contain both the tetragonal and orthorhombic structures at room temperature. Owing to the more possible polarization states arising from the coexistence of the two phases, the piezoelectric and dielectric properties of the ceramics are enhanced significantly.