Aqueous processing of barium titanate powders

In many modem electronic devices, multi-layer ceramic capacitors (MLCCs) are used in large quantities. For a greater volume efficiency of MLCCs, current efforts include thinner dielectric layers and a larger number of layers in a given volume, together with embedded-capacitor design. All of these require a smaller particle size of the raw ceramic material, barium titanate (BaTiO3) powders, with closely controlled particle morphology and processing behavior. The current state-of-the-art technology for MLCCs utilize non-aqueous or solvent-based processing. For a cleaner environment and a greater cost effectiveness of the processing, development of water-based processing technology for MLCCs is more imperative than ever. As the miniaturization of electronic devices continues to demand smaller particle size powders with controlled morphology, the desired characteristics of the starting powder becomes a critical issue. Among the methods to produce sub-micrometer BaTiO3 powder (BT), hydrothermal synthesis has been shown to have an edge. However, hydrothermal BT is expensive and exhibits sintering problems due to the large amount of lattice hydroxyls which were incorporated during its aqueous-based synthesis process. A new synthetic method; Ambient Condition Sol (ACS) process has been considered in our laboratory which is to decrease the amount of incorporated hydroxyl ions in a water-free synthetic medium. The increasing difficulty of dispersion and stability of nanometer-sized BT particles is mitigated by introducing a steric barrier layer during the ACS synthesis, resulting in a re-dispersible particles in water. This concept was further demonstrated in the surface passivation of BT particles in water by reducing the Ba2+ ion leaching over an extended period of time, The results showed the Ba2+ leaching rate to be an inverse function of the solution pH and a direct function of the organic adsorption isotherm onto the BaTiO3 surface. The effectiveness of organic passivation agents was directly proportional to the pH of the medium. The BT particle morphology, degree of passivation, evidence of lower concentration of lattice hydroxyl impurity, the kinetics of ACS synthesis for BT, redispersibility, and the resulting phase analyses are reported.