PARTICLE SIZE AND MORPHOLOGY CONTROL OF PEROVSKITE OXIDE NANOPOWDERS FOR NANOSTRUCTURED MATERIALS

Abstract

ABSTRACT Due to the high permittivity and low losses, ferroelectric ceramics with perovskite structure are largely used in the electronics industry for many applications. Presently, miniaturization of the components is one of the main goal in the field of microelectronics and communication. Accordingly, the current trend in high-tech ceramics is to realize sintered bodies with grain size below a few hundred of nanometres. This aim can be attained using high-quality nanopowders (≈100 nm) with narrow particle size distribution (PSD), that allows low-temperature sintering at high densification and limited grain growth. Soft chemistry methods are presently receiving increasing interest. Ultra-fine, non-agglomerated BaTiO3 (BT) and SrTiO3 (ST) nanopowders with PSD were prepared considering the thermodynamic conditions for direct precipitation from the relevant metal chlorides in strong alkaline aqueous solution (T ≈ 45 ÷ 95 °C, P = 105 Pa, pH ≈ 14). Nuclei formation, crystallite growth and aggregation of crystallites were controlled to get high-quality powders. Strict control of supersaturation and temperature reduces the heterogeneity and allows a good control of cations concentration which determines the final particle size. Tailoring (15 ÷ 1500 nm) of BT, ST and other perovskites nanopowders with narrow PSD and good stoichiometry control was obtained. For high quality nanoceramics fast densification procedures are required to prevent grain growth. By Spark Plasma Sintering (SPS) high density nanocrystalline BT ceramics down to 30 nm at high density and excellent dielectric characteristics were obtained with interesting dielectric properties. Core-shell powders of various perovskite oxides were also prepared.