Tailoring of perovskite oxides nanopowders: particles size and morphology control to produce nanocrystalline dense ceramics

The current trend in advanced ceramics is to realize grain size below a few hundred of nanometers. This aim can be attained if high quality nanopowders (~100 nm) with narrow particle size distribution are available for which also relatively low-temperature sintering is also required to reach high densification whilst preventing grain growth. An original and innovative approach in producing high quality perovskite non-agglomerated nanopowders, with a strict control of stoichiometry, narrow particle size distribution by soft chemistry methods is presented. Ultra-fine, non-agglomerated BaTiO3 and SrTiO3 nanopowders with sharp particle size distribution were prepared by direct precipitation of the relevant metal chlorides dissolved in a strong alkaline aqueous solution by considering the thermodynamic conditions stated for these aqueous syntheses. Since the preparation of nanopowders is very sensible to the synthesis parameters, critical points such as nuclei formation, crystallite growth and aggregation of crystallites were strictly controlled. Particularly a strict control of supersaturation and temperature strongly reduces the heterogeneity conditions of the reactor and makes possible to control the cations concentration which determines the final particle size. We succeeded in tailoring BaTiO3 and SrTiO3 nanopowders in the range 15 ÷1500 nm, with a narrow particle size distribution and a high stoichiometry control.