Nanostructured Nb doped PZT powders via sol-gel auto-combustion

Nanocrystalline niobium doped lead zirconate titanate powders (PZTN) were prepared by a citrate-nitrate sol-gel combustion technique. The combustion involves a heat-induced exothermic oxidation-reduction reaction between carboxyl groups and nitrate ions. The technique involves three steps: formation of stable and homogeneous sol; formation of aereogel; combustion of aereogel. The preparation of sol was performed by mixing stable solutions of Zr-oxynitrate, Pb-citrate, Nb- and Ti-peroxo-citrate precursors. The thermal decomposition of gel was investigated by DTA-TG and FTIR. The combustion process was confirmed by the exothermic profile of DTA analysis in comparison with the endothermic peaks of raw materials decomposition. The structural characteristics of the resulting powder were characterized by XRD and SEM analysis. The auto ignited combustion leads to the decomposition of precursors and the formation of pure perovskite phase after treatment at 400°C for 4h. The particles were found to be irregular aggregates of nanometric primary particles (crystallite size about 30nm). Different milling treatments were performed in order to improve the sinterability. Ball milled (100h with PEG) powders sintered at 1100°C for 2h in air show 97% relative density at a densification T 100°C lower than for the conventional mixed oxide route. The stoichiometry of the systems was controlled at each stage of the process and no fluctuation was detected.