Size‐Dependent Crystal Properties of Nanocuprite

Cuprite nanoparticles from 9 nm to 1 μm 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 Cu 2 O 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.