Size-Dependent Crystal Properties of Nanocuprite

Cuprite nanoparticles from 9 nm to 1 m with narrow size distribution (+/- 7%) are prepared by two different methods. The lattice parameter increases up to 0.2% as the crystallite size decreases to 9 nm from micron size. X-ray Absorption Near Edge Spectroscope study of our copper oxide nanoparticles shows mostly Cu (I) with increasing concentration of Cu (II) as decreasing crystal sizes. The size effect in Cu(II)/Cu(I) ratio indicates that at smaller crystal size, the Cu2O tends to be more oxidized at higher charge state with Cu(I)-O bond. Thus, the lattice expansion can be explained by the presence of longer Cu (II)-O bond than Cu (I)-O bond and/or oxygen interstitials in nanocuprite.