Abstract: CuCr_1-xMg_xO₂(x=0, 0.005, 0.010, 0.020, 0.030, 0.040, 0.050) polycrystals with c-axis preferred orientation were prepared by solid phase reaction method. The effects of Mg²⁺ doping on the microstructure orientation, electrical properties, and anisotropy of CuCrO₂ polycrystals from the vertical and parallel macroscopic in-plane and thickness directions were investigated. The mechanism of Mg doping enhancing the anisotropy of the electrical conductivity in CuCrO₂ ceramics was explored. When x≤0.030, the polycrystals exhibit a rhombohedral R3m single-phase structure, with grain growth predominantly occurring within the surface plane. This led to a reduction in the presence of gas pores and grain boundaries, resulting in the increase of density. The polycrystals demonstrated thermally activated semiconductor electrical transport behavior. When x=0.030, the in-plane orientation factor F_(00l) reaches its highest value of 0.912, indicating a significantly enhanced c-axis preferred orientation within the surface plane compared to the thickness direction. The room temperature resistivity of CuCr_1-xMg_xO₂ polycrystals in the in-plane and thickness directions decrease significantly to 1.80×10^-3 and 3.16×10^-3 Ω·m, respectively. This difference in electrical performance between the two directions was closely related to the structural anisotropy. The thermal activation energy decreased to 0.03 eV, and the c-axis preferred orientation has no significant influence on the thermal activation energy. The maximum carrier concentration increase by three orders of magnitude compared to the parent phase, indicating fewer grain boundary defects, an increased average free path, enhanced transport capacity, and higher conductivity. The experimental results reveal that the optimal doping concentration is x=0.030. When the doping level exceeded 0.030, the spinel phase MgCr₂O₄ appeared as an impurity, resulting in a deterioration of the microstructure and electrical transport properties of the samples.

Key words: c-axis preferred orientation, CuCr_1-xMg_xO₂ polycrystalline, anisotropy, resistivity, grain boundary defect, electrical transportation