Colloidal processing of PMN-PT thick films for piezoelectric sensor applications

65%Pb(Mg1/3Nb2/3)O3-35%PbTiO3 (65PMN-35PT, or PMN-PT) is a highly piezoelectric ceramic with superior piezoelectric coefficients over the more popular Pb(Zr0.5Ti0.5)O3 (PZT). Because of its complex chemistry and high volatility of lead above 1000°C, the perovskite phase of PMN-PT is hard to process and has prevented PMN-PT from various piezoelectric applications, especially in the new area of piezoelectric micro-electro-mechanical systems (PMEMS) involving thick or thin piezoelectric films. In this thesis, a novel precursor suspension method is introduced that substantially lowers the sintering temperature of PMN-PT to 850°C from a PMN precursor power made by coating Mg(OH)2 on Nb2O5 particles. The precursor suspension method entails suspending PMN powders in PT precursor and uses the reaction sintering capability of PMN with nano-sized PT in the temperature range of 800°C~1000°C. Moreover, free-standing PMN-PT thick films were obtained by tape casting the PMN-PT powder. This new geometry of PMN-PT shows giant electric-field enhanced piezoelectric responses comparable with those of single crystals. As an example of application, the PMN-PT thick film is bonded to a thinner layer of copper by electroplating and made into piezoelectric cantilever sensors. In conclusion, the colloidal suspension processing method produces free-standing PMN-PT thick films with ultrahigh piezoelectric properties.