Structures and the oxygen deficiency of tetragonal and monoclinic zirconium oxide nanoparticles.

The crystal structure of zirconium oxide nanoparticles was refined by the Rietveld analysis of synchrotron X-ray powder diffraction data measured at 298 K. In the nanoparticles, two phases of tetragonal ZrO(2 - delta) (average particle size: 11 +/- 2 nm) and monoclinic ZrO2 (average particle size: 24 +/- 4 nm) existed, where the weight fractions were estimated to be 84.9 and 15.1 wt%, respectively. The structural refinement suggests that the tetragonal ZrO(2 - delta) has an oxygen deficiency [delta = 0.031 (7)] and that the monoclinic ZrO(2 - delta) has less oxygen deficiency (delta approximately 0), where delta is the vacancy concentration. The monoclinic ZrO2 has a larger unit-cell volume. The maximum-entropy method analysis indicated covalent bonding between Zr and O atoms.