Electronic transport properties of hole-doped Sr_1+xLa_1-xCrO_4+δ

Polycrystalline bodies of Sr_1+xLa_1-xCrO_4+δ (0≤x≤0.3) with a K₂NiF₄ structure were prepared and the temperature dependence of the electrical conductivity and Seebeck voltage at room temperature were measured. The temperature dependence of conductivity followed a functional form of exp [( - T₀/T) ^α] (α=1/3 or 1/4 ), which was characteristic of two- or three-dimensional variable-range hopping (VRH) model. The hopping conductivity showed that the crystal was non-metallic because the electronic states at the Fermi energy were localized. Values of T₀ in the three-dimensional VRH regime were in the range of 1-5 × 10⁸ K. This was larger by two orders of magnitude than reported values in La₂CuO₄ which was insulating between room temperature and 2 K. Based on the VRH regime, the larger T₀ values were considered to be caused by the smaller localization radius of impurity states. All the samples were demonstrated to have a positive Seebeck coefficient. Further, the coefficient decreased with increasing doping level. The composition dependence of the Seebeck coefficient was discussed in relation to the changes with compositions in T₀ and the density of states in the vicinity of the Fermi energy.