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

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.