In-situ X-ray photoelectron spectroscopic study of the reversible phase transition between CoO and Co3O4 in oxygen of 10−3 Pa

Abstract

The temperature dependence of the Co 2p and O 1s XPS spectra for the cobalt-oxygen system was studied in an oxygen atmosphere of 1 × 10 −3 Pa. The reversible transition between CoO and Co 3 O 4 was observed between 373 and 973 K. Although bulk thermodynamics predicts a transition temperature of 806 K, the transition occurred at about 620 K. This means that surface compositions or phases of the Co-O system are ruled by surface thermodynamics different from that of the bulk.