| The use of additives (dopants) that are incorporated into solid solution forms the most effective approach for controlling the microstructure and, hence, the engineering properties of advanced ceramics. However, except for a few well recognized systems (e.g., MgO-doped {dollar}rm Alsb2Osb3),{dollar} the role of the additives during sintering is not clear. This limits the applicability of the approach to a trial and error basis. The present work forms an attempt to extend the understanding of the dopant role during sintering to the {dollar}rm BaTiOsb3{dollar} system. A combined approach consisting of survey studies for valid generalization and detailed studies of individual systems to obtain a full picture of a particular interaction is employed. The results are described in three papers. In the first paper, the effect of aliovalent cations that differ in ionic radius and valence on the densification and grain growth of BaTiO{dollar}sb3{dollar} is described. Except for cations that lead to the formation of a liquid or volatile second phase during sintering, all acceptor cations inhibit grain growth. Donor dopants enhance grain growth below a doping threshold of 0.3 to 0.5 at % but significantly retard grain growth above the doping threshold. The second paper describes detailed studies of the influence of two donor cations {dollar}rm (Nbsp{lcub}5+{rcub} for Tisp{lcub}4+{rcub} and Lasp{lcub}3+{rcub} for Basp{lcub}2+{rcub}){dollar} and an acceptor cation {dollar}rm (Cosp{lcub}2+{rcub} for Tisp{lcub}4+{rcub}).{dollar} The results show that the most important effect of the dopants is their ability to influence the grain boundary mobility. The dopant roles are interpreted in terms of segregation at the grain boundaries by a space-charge mechanism (acceptors) and their effect on the lattice defect chemistry (donors). In the third paper, the influence of the dopant cations on the dielectric properties (Curie temperature, dielectric constant and dielectric loss tangent) of the sintered BaTiO{dollar}sb3{dollar} materials is explored in an attempt to characterize the structural changes produced by the dopants. |
