Preparation of Cr-Doped V₂O₃ Films by Sol-Gel Processing and Their Resistivity-Temperature Characteristics

Abstract

Films of Cr-added V₂O₃ were prepared by reduction of sol-gel-derived V₂O₅ films at temperatures over 500°C in flowing H₂. Auger electron spectroscopy of the films showed that atoms of V and O were distributed homogeneously on thickness direction. From X-ray photoelectron spectroscopy of the films, it was found that the reduction was enhanced with an increase of the reduction temperature, however, even at 900°C reduction valence of V still interposed between +3 and +4. The specific resistivity (ρ)-temperature (T) curves of the films showed antiferromagnetic insulator (AFI)-metal (M) transitions, but not metal (M)-insulator (I) transitions. Grain diameters of Cr-doped V₂O₃ powders prepared in the same way of the films increased by sintering at 1000 to 1350°C for 5h in flowing mixture gas (95vol%N₂+5vol%H₂). The M-I transitions was observed in the ρ-T curves of these powders heated at 1200°C and higher. Absence of M-I transition of sol-gel-derived V₂O₃ films was considered to be due to small grain sizes and/or small crystallite size of films.