Synthesis and piezoelectric properties of nanocrystalline PZT-based ceramics prepared by high energy ball milling process

Nanocrystalline powders of a soft FeNbLi-doped PZT material have been prepared by a novel mechanochemical process consisting of mixing the stoichiometric oxides in a planetary ball mill for prolonged times up to 80 h. The constituent oxides were reacted in a tungsten carbide vial with balls of 5, 10 and 20 mm in diameter and a ball/powder ratio of 15/1. The chemical reaction between the component oxides was triggered after 20 h of energetic milling and was completed after 80 h. The XRD of the reacted nanopowder showed the well known perovskite structure. Compacted samples of this powder were sintered between 800-1300°C for 3 h and the main piezoelectric properties were determined. The density of the sintered samples reached nearly 99% of the theoretical density at 1100°C and showed good piezoelectric characteristics: planar coupling factor of 0.66, dielectric displacement constant d33 of 550 pm/V, mechanical quality factor of 85, and relative dielectric constant of 3800. The possible mechanisms for solid state reaction of mechanically activated nanopowders such as local heating and pressure at collision as well as defects diffusion are discussed.