• Neck, V.
• Dardenne, Kathy
• Rothe, Joerg
• Walther, C.
• Fanghänel, T.
• Denecke, M. A.
• Cho, H. R.

Abstract

    Analysis of EXAFS data shows the structure of the microcrystalline colloids in a 0.1 mol l-1 Zr aqueous solution at pH 0.2 to contain tetrameric units, similar to those in ZrOCl2 × 8H2O. Characterization of the coulometric titration solutions by means of EXAFS shows that oligomeric species form as the solubility limit is approached (Fig. 1). None of the spectra for samples with pH 2 and higher resemble that for monoclinic ZrO2, the stable colloids at pH 0.2 or the starting solution at pH 1. We conclude that the Zr in these titration samples must have a different structure than in these other compounds and solution samples. The structure of these solution species is not a simple ZrO2; it has neither the monoclinic, cubic, orthorhombic, nor tetragonal ZrO2 structure. Its structure also cannot be derived from simple stacking of tetrameric [Zr4(OH)8(H2O)16]8+ units. The Zr-O coordination number of the polynuclear species in the samples with pH ¡Ý2 is near eight and its distance shows little variation. At the same time, the Zr-Zr interaction is relatively small and this coordination shell is possibly comprised of more than one distance. We interpret these results as indicating that the species are built up of primarily ZrO8 building blocks, but the associated Zr sublattice is highly disordered. Polymerization and packing into a more condensed system is likely leading to a disordered and    

Topics

• impedance spectroscopy
• compound
• titration
• extended X-ray absorption fine structure spectroscopy