Mechanosynthesis and thermal stability of piezoelectric perovskite 0.92Pb(Zn1/3Nb2/3)O3-0.08PbTiO3 powders

The mechanosynthesis of piezoelectric perovskite 0.92Pb(Zn1/3Nb2/3)O-3-0.08PbTiO(3) (PZN-PT) by direct mechanochemical activation of the constituent oxides has been studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM). This and the PbO flux method are the only two procedures that have succeeded in synthesizing this phase, which has recently been shown to present very high electromechanical response. The thermal stability of the single perovskite phase powders has been studied by differential thermal analysis/thermogravimetry and by high-temperature XRD as a function of mechanical activation time and pressure. The phase was found to transform into a pyrochlore type structure at temperatures above 400degreesC. The transformation presented a significant time dependence, and it was slowed down by increasing mechanical activation time and by the application of pressures by hot pressing. Sintering experiments were accomplished and 85% density, 77% perovskite-phase ceramics were obtained after heating at 1000degreesC for I h. Hot pressing at this temperature failed to increase the percentage of perovskite phase. Results are discussed, and procedures for obtaining dense single-phase PZN-PT-based ceramics with ultrahigh piezoelectricity are proposed.