Conventional and microwave sintering studies of SrTiO₃

Using the nonconventional sintering technique, such as microwave sintering, it is observed to enhance the densification rate of SrTiO₃ materials as effectively as employing the highly active powders prepared by the chemical route. Although the chemically derived powders demonstrate better sinterability than the mixed oxide powders, the thermal analysis indicates that the segregation of Ti⁴⁺-containing clusters during decomposition of precursors in the direct pyrolysis (DP) process induces the occurrence of TiO₂ particles (anatase phase) prior to the formation of SrTiO₃ phase. These particles retard the necking process required to sinter the materials. The spray pyrolysis (SP) process can circumvent the preferential nucleation of TiO₂ phase and, therefore, produce powders exhibiting superior sintering behavior to the DP-derived powders. The microwave sintering technique, on the other hand, substantially enhances the rate of diffusion of the ions in the materials such that even the mixed oxide powders can be sintered at a temperature about 200 °C lower than that needed to achieve the same density in a conventional sintering process. Fine grain (∼4 μm) microstructure is obtained for the materials microwave sintered at 1220 °C for 10 min. The migration of grain boundaries requires higher temperature to initiate than the formation of neckings between the grains. The grain growth occurs only when the material was sintered at temperatures higher than 1250 °C.