粉体から作製したTa_2O_5-TiO_2セラミックスの緻密化と粒成長(論文,希土類系物質の精密合成,形態制御および機能物性)

概要

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Thermal processing of powder-derived Ta_2O_5-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-Ta_2O_5) and a phase which is stable at high temperatures (H-Ta_2O_5). The H-Ta_2O_5 phase is metastable at room temperature and reverts back to the L-Ta_2O_5 phase with thermal or mechanical treatment. TiO_2 additions stabilize the H-Ta_2O_5 phase and result in enhanced dielectric properties. Because TiO_2 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 TiO_2-modified Ta_2O_5 ceramics in both the L- and H-Ta_2O_5 forms. Thus, this work represents the first comprehensive study of the effects of composition and the L⇒H-Ta_2O_5 phase transformation on microstructural development. The results indicate that the effect of TiO_2 additions on the sintering behavior of Ta_2O_5 ceramics was largely limited to a reduction in the temperature for the densification-hindering phase transformation.
2007-10-01