Study on Microstructures and Electrical Properties of Na0.52K0.48NbO3-base Lead-free Ceramics

• Main Authors: Yang-Yao Liu, 劉陽耀
• Other Authors: 曾俊元
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/d492mw

碩士 === 國立臺北科技大學 === 材料科學與工程研究所 === 96 === Some materials containing with harmful health elements such as lead(Pb), cadmium(Cd), mercury(Hg), hexavalent chromium(Cr VI), are recently inhibited for industrial applications because of the consideration of environmental protection. At present, the most important piezoelectric ceramics is PZT, which contains Pb content. It needs to find other Pb-free piezoelectric, but owning to the difficulty of finding ceramics to substitute PZT. One of possible candidates is NKN ceramics. However, (Na0.52K0.48)NbO3 ceramics sintered by ordinary sintering show relatively lower electrical properties due to the difficulty in obtaining dense ceramics by ordinary sintering in air. The phase stability is for potassium sodium niobate limited to 1140℃. High temperatures of sintering of NKN is therefore impossible to achieve dense ceramics. Furthermore, the volatility of potassium oxide makes its stoichiometry difficult to control the formation of extra phases leading to a quick disintegration of the final samples once exposed to humidity. Modified potassium sodium niobate ceramic have good properties such as high Curie point (Tc), high temperature stability and high electromechanical constant (kp、kt), which is suitable to be used as surface acoustic wave (SAW) gas sensors. In this work, CaTiO3 is doped into (Na0.52K0.48)NbO3 to form the modified potassium sodium niobate ceramic system by the conventional oxide-mixed method. The effect of processing parameters on the properties of the ceramics is studied to find the optimal processing conditions. (1-x) (Na0.52K0.48)NbO3-x CaTiO3 [x=0~1] ceramics can successfully be synthesized in this study. X-ray patterns of these ceramics show that all the samples belong to pure perovskite phase and no extra-peaks can be identified. We also study the phase transformation with composition variation of this system. The structure of the phase is changed from Octahedral phase to Tetragonal phase, when x between 0.03 and 0.07. Besides, the lattice parameters and theoretical densities of the ceramics are also obtained based on the data obtaining from XRD study. It is shown that the piezoelectric properties of these ceramics near the morphotropic phase boundary (MPB) region are superior than those of the ceramics on the other regions.