Investigation of coordination state of Zr 4+ ions in the sol—gel-derived ZrO 2SiO 2 glasses by EXAFS

Abstract

The coordination state Zr 4+ ions in sol—gel-derived ZrO 2SiO 2 glasses of different ZrO 2 contents was examined using EXAFS. Two types of ZrO bonds were found in the first coordination shell. In the gels, Zr 4+ ions were coordinated by approximately four oxygens. One of the four oxygens was located at a distance of about 2.08 Å from Zr 4+ ion, forming a bridging ZrO bond. The others were at about 2.63 Å, and are attributed to non-bridging ZrO bonds (probably ZrOH). As a temperature was increased the coordination number of Zr 4+ ions with respect to oxygens increased to about 5 owing to the increase of bridging oxygens. The number of bridging oxygens around a Zr 4+ ion was increased from unity to three or four, and the number of non-bridging oxygens was decreased, at a smaller rate than that of the increase of bridging oxygens.