Microstructural characterization of grain-oriented glass-ceramics in the system Ba2TiSi2O8-SiO2

In polycrystalline fresnoite, advantage of the piezo- and pyroelectric prop erties can be taken only if texturing along its polar [0 0 1]-axis can be a chieved. We report on a novel technique to prepare grain-oriented glass-cer amics in the system fresnoite-SiO2 by electrochemically induced nucleation. Optimum conditions for grain orientation were determined by characterizing the microstructure of glass-ceramics prepared at 1150, 1200 and 1350 degre es C using electron microscopy and X-ray texture goniometry. At 1150 degree s C-due to the smallest crystal growth rate and highest nucleation rate-the most distinct orientation is obtained. The solidification of the glass-cer amic consist of three subsequent steps. First, dendritic fresnoite crystall izes most rapidly along its [0 0 1]-axis with {1 1 0} facet planes. Due to growth selection, the polar c-axes become oriented. Secondly, within the in terdendritic areas, the pseudo-binary eutectic fresnoite-silica solidifies lamellarly. Finally, in the middle of the interspaces, a crystalline barium silicate coexisting with glassy silica is formed at 1200 degrees C and 135 0 degrees C. At 1150 degrees C, however, a glass with the composition of th e melt solidifies. (C) 1999 Kluwer Academic Publishers.