1. Jaffe B, Cook WR, Jaffe H. Piezoelectric Ceramics. New York: Academic Press, 1971.
2. Eu-Directive 2002/96/Ec: Waste electrical and electronic equipment (WEEE). Off J Eur Union 2003, 46: 24–38.
3. Eu-Directive 2002/95/Ec: Restriction of the use of certain hazardous substances in electrical and electronic equipment (RoHS). Off J Eur Union 2003, 46: 19–23.
4. Saito Y, Takao H, Tani T, et al. Lead-free piezoceramics. Nature 2004, 432: 84–87.
5. Guo YP, Kakimoto K, Ohsato H. Phase transitional behavior and piezoelectric properties of (Na0.5K0.5)NbO3-LiNbO3 ceramics. Appl Phys Lett 2004, 85: 4121–4123.