Densification and Grain Growth for Powder-Derived Ta₂O₅-TiO₂ Ceramics

抄録

Thermal processing of powder-derived Ta₂O₅-based ceramics reveals that rapid grain growth associated with a high temperature phase transformation hinders densification, necessitating the development of a reduced-temperature processing methodology. Data are reported for the densification behavior with emphasis on microstructural changes associated with the phase transformation between a stable low-temperature phase (L-Ta₂O₅) and a phase which is stable at high temperatures (H-Ta₂O₅). The H-Ta₂O₅ phase is metastable at room temperature and reverts back to the L-Ta₂O₅ phase with thermal or mechanical treatment. TiO₂ additions stabilize the H-Ta₂O₅ phase and result in enhanced dielectric properties. Because TiO₂ additions decrease the temperature of the densification-hindering phase transformation, an alternate reduced-temperature processing route is necessary. A simple solution-coated powder method was used to produce the first-ever dense and chemically homogeneous TiO₂-modified Ta₂O₅ ceramics in both the L- and H-Ta₂O₅ forms. Thus, this work represents the first comprehensive study of the effects of composition and the L⇒H-Ta₂O₅ phase transformation on microstructural development. The results indicate that the effect of TiO₂ additions on the sintering behavior of Ta₂O₅ ceramics was largely limited to a reduction in the temperature for the densification-hindering phase transformation.