The objective of this dissertation is to investigate the relationship between the processing parameters, microstructural development, defect chemistry and electrical properties of titanium oxide (TiO₂) dielectrics for high energy density capacitor applications. The effects of aliovalent dopants on the dielectric properties of TiO₂ ceramics were investigated, aiming to further improve the desired dielectric properties especially at elevated temperatures (up to 200°C). Due to the segregation of acceptor type impurities in the starting powders, space charge polarization took place in TiO₂ ceramics with relative large grain size (\u3e̲500nm), leading to high dielectric loss and low energy storage efficiency. Increased ratio of grain boundary resistivity to bulk grain resistivity resulted in lower breakdown strength, as larger electric field was applied on the grain boundaries as they became the most resistive part. Donor doping (e.g phosphorus or vanadium) can effectively remove the space charge layer due to charge neutralization of positively charged defects created by donors and negatively charged defects created by acceptors. Large area, crack free tapes were fabricated by tape-casting method using nano-sized (~40nm) TiO₂ powders. An energy density of ~14 J/cm³ was demonstrated by testing of TiO₂ thick films (~100µm).
Studies on dielectric materials were extended to BaTiO₃/SrTiO₃ (BST) ceramics which were processed by lamination of BaTiO₃ and SrTiO₃ green tapes with a 2-2 spatial configuration. Preliminary results showed that BST ceramics are promising dielectrics for energy storage applications and offer compositional flexibility to achieve maximum energy density under specified electric fields --Abstract, page iv
