Formation of stable Cu2O nanocrystals in a new orthorhombic crystal structure

Substantially stable Cu2O nanocrystals of 10-30 nm in size have been synthe sised by an ion exchange Cu2+ --> Cu --> Cu+ reaction in an aqueous solutio n (using a reducing agent NaBH4) at 80-100 degreesC. In so small particles, a large fraction of surface atoms, i.e. 20% or even more, which suffer wit h a reduced coordination number of the core atoms, support the formation of the low oxidation state Cu2O oxide of copper in a stable structure. Otherw ise, CuO is the most stable form of its oxides. The 10-30 nm Cu2O nanocryst als have a modified X-ray diffractogam of FCC bulk Cu2O structure. The diff ractogram is very simple with a total of only seven peaks, over 0.25-0.12 n m d(hkt) interplanar spacing, which are successfully indexed assuming an or thorhombic crystal structure with lattice parameters a = 0.421 nm, b = 0.32 3 nm and c = 0.361 nm (at 25 nm size of the sample). (C) 2001 Elsevier Scie nce B.V. All rights reserved.