The electrical,optical and photoconducting properties of Fe2−xCrxO3 (0 ⩽ x ⩽ 0.47)

A study has been made of the electrical, optical and photoconducting properties of pure and reduced single crystals of composition Fe_2?xCr_xO₃ where 0 ? x ? 0.47. It has been found that pure α-Fe₂O₃ is not a photoconductor. When defect-free crystals of α-Fe₂O₃ are reduced a surface layer of Fe₃O₄ is formed and the crystals exhibit photoconductivity. Removal of this layer resulted in the disappearance of photocurrents and an increase in the sample resistivity. A necessary condition for the observation of photocurrents in n-type Fe₂O₃ is that some Fe₃O₄ be present. In addition, it has been found that the substitution of chromium for iron in α-Fe₂O₃ results in a monotonically decreasing optical band gap as the chromium concentration, x, increases.