DOPANT REDUCTION IN P-TYPE OXIDE-FILMS UPON OXYGEN ABSORPTION

The lower valent cations were homogeneously doped in p-type oxide film s. The prepared doped oxide systems were Mg-doped alpha-Cr2O3, Ni-dope d alpha-Cr2O3, and Li-doped NiO. The Mg doping induced a homogeneous m ixed valence state of Cr3+ and Cr6+ in the Cr2O3 film, reducing the Mg dopant to the metallic valence state in the Cr2O3 lattice, which is c ompletely different from the powder or single crystalline system. The mixed valence state formation gave rise to a marked chromism. The mixe d valence formation and perfect reduction of the lower valent dopants were evidenced by X-ray photoelectron spectroscopy, electrical conduct ivity change, and optical absorption. Ni-doped alpha-Cr2O3 and Li-dope d NiO showed similar results. The reduction kinetics of the mixed vale nce state in the p-type oxide lattice with the aid of the electrical c onductivity measurement suggested that the rate-determining step is no t the diffusion of oxygen.