X-ray diffraction and X-ray absorption spectroscopy studies of sol-gel-processed zirconium titanates

ZrTiO4 samples were prepared by using a conventional hydrolytic alkoxide sol-gel route, a nonhydrolytic method, an acetic acid modified route, and by the direct reaction of the binary oxides. The local structure in the gels and its evolution upon heating was followed using EXAFS and XANES, and the crystallization of the products was examined using powder X-ray diffraction. All the solution-processed materials crystallized in the range 600-700 degreesC. The crystalline materials formed at 700 degreesC showed no evidence of any long-range cation ordering. The EXAFS data indicated that all the amorphous ZrTiO4 samples produced using the solution routes contained zirconium with a coordination number >6 and that the disordered crystalline ZrTiO4 contained six-coordinate zirconium. Both the XANES and EXAFS data showed that nearly all the amorphous ZrTiO4 samples contained titanium with a coordination number of <6. The EXAFS data clearly indicated the presence of Zr-O-Ti links in the ZrTiO4 gel produced using the nonhydrolytic route. There was also some evidence that the gel prepared using hydrolytic sol-gel chemistry contained Zr-O-Ti links.