Electron-microscopic study of the structure of metastable oxides formed in the initial stage of copper oxidation. III. Cu₆₄O

Abstract

Besides Cu40 and CusO reported previously, a third metastable copper oxide with the chemical composition Cu640 formed in the early stage of oxidation of copper has been observed by high-resolution electron microscopy. The atomic positions of Cu and O have been determined by electron diffraction and by comparison of the observed structure images with simulated ones calculated on the basis of the dynamical theory of electron diffraction and image formation theory. Cu640 is ordered base-centered orthorhombic with lattice constants a =9.74, b = 10.58 and c= 16.20 A. The intensity of the diffracted waves reflecting the periodicity of the O-atom arrangement in Cu640 is much weaker than those in Cu40 and Cu80 because of the lower oxygen content. Thus, the images of O atoms in the Cu640 crystal can only be observed at limited thicknesses. Good agreement between the observed and calculated images has been obtained, though the distance between the Cu atoms in Cu640 is still too small to be resolved.