Zusammenfassung :

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

defect-rich Zr sublattice.