Dopant Reduction in p-Type Oxide Films upon Oxygen Absorption

The lower valent cations were homogeneously doped in p-type oxide films. The prepared doped oxide systems were Mg-doped α-Cr 2 O 3, Ni-doped α-Cr 2 O 3, and Li-doped NiO. The Mg doping induced a homogeneous mixed valence state of Cr 3+ and Cr 6+ in the Cr 2 O 3 film, reducing the Mg dopant to the metallic valence state in the Cr 2 O 3 lattice, which is completely different from the powder or single crystalline system. The mixed valence state formation gave rise to a marked chromism. The mixed valence formation and perfect reduction of the lower valent dopants were evidenced by X-ray photoelectron spectroscopy, electrical conductivity change, and optical absorption. Ni-doped α-Cr 2 O 3 and Li-doped NiO showed similar results. The reduction kinetics of the mixed valence state in the p-type oxide lattice with the aid of the electrical conductivity measurement suggested that the rate-determining step is not the diffusion of oxygen.