"Synthesis of Nb doped PZT by chemical methods"

Nb-doped lead zirconate titanate powders (PZTN) were synthesized starting from an aqueous solution of precursor salts. The thermal and structural evolution of precursors processed through a sol-gel combustion technique was compared with precursors obtained by the spray-drying of the salts solution and by the coprecipitation of hydroxides. The sol-gel synthesis is based upon the auto-combustion of a citrate-nitrate gel at 400°C where the perovskitic phase resulted almost fully reacted. The precursor salts (Pb and ZrO nitrates, Ti isopropoxide and Nb ammonium oxalate) were complexed with ammonium citrate at pH 7 and H2O2 was used to stabilize Ti and Nb complex. The transparent gel was formed upon slow water evaporation and then submitted to thermal treatment. The precursor powder by spray drying was obtained by preparing a water solution of Pb and ZrO nitrates, Ti isopropoxide and Nb-ammonium oxalate, spraying it in a hot chamber at 200°C and collecting the resulting dried powder that transformed to perovskite phase after calcination at 550°C. The mixture of coprecipitated hydroxides was obtained by dropping Pb nitrate ZrO chloride and TiCl4 stabilized with H2O2 in a NH4OH solution ( pH range 9-10). Nb salt was not added to this synthesis. The collected powder was filtered, washed several times in order to eliminate Cl- and NO3- ions and dried at 100°C. In this case no formation of perovskite phase was detected after calcination at 600°C where the intermediate phases (PbTiO3, ZrO2, Pb3O2Cl2) were still present. The thermal evolution of precursors powders was investigated through the TG/DTA analysis and comparing IR, Raman and XRD spectra collected at different temperatures. The morphologies of PZT powders obtained by sol-gel and spray-drying were observed by SEM and related to the synthesis mechanism.