The effect of zirconia content on the structure of zirconia-silica xerogels as determined by x-ray and neutron diffraction and ZrK-edge EXAFS and XANES

We present combined x-ray and neutron diffraction, and extended x-ray absor ption fine structure (EXAFS) and x-ray absorption near edge structure (XANE S) results on a single set of (ZrO2)(x)(SiO2)(1-x) xerogel samples. In thes e samples, there is improved homogeneity of Zr compared to our previous stu dy, due to greater dilution of the precursor Zr n-propoxide in propan-1-ol. Structural parameters obtained from model fitting of the diffraction and E XAFS data are compared with those in reference compounds. A qualitative com parison df XANES spectra is also made. The results show that for x greater than or equal to 0.3 there is phase separation of ZrO2 and the Zr environme nt is similar to that in monoclinic ZrO2 and Zr hydroxide. For x less than or equal to 0.2 there is no phase separation, the SiO2 network is distorted and the Zr coordination is similar to that in Zr n-propoxide, with some Zr -Zr clustering.