Solid solubility of Mg and enhanced electrical conduction in the C-axis orientation of CuCr_1-xMg_xO₂ polycrystals

The c-axis orientation of CuCr1-xMgxO2 (0 ≤ x ≤ 0.08) ceramics was prepared through solid-state reactions. The effects of a Mg solid solution in CuCrO2 have been investigated in terms of electrical conductivity, thermopower, and microstructure. While x = 0–0.03, the polycrystalline grains in a single-phase delafossite grew along the ab-plane with increasing (00 l) Lotgering factors of up to 0.53. It exhibited semiconducting electrical transport. The room temperature conductivity increased by 3–4 orders of magnitude, even up to 12.03 S·cm−1, because of a reduction in Arrhenius activation energy. The Seebeck coefficient decreased from 828 to 257.8 μV·K−1 at 330 K. For the doped samples, due to the contribution of the phonon drag thermopower overmatching the variation of the carrier concentration to the thermopower, it increased with increasing temperature, which was the opposite to that observed in the undoped samples. While x = 0.04–0.08, the second-phase MgCr2O4 spinel appeared and the properties and microstructure hardly changed. The layered structure of the c-axis orientation led to dominant electrical transport along the ab-plane and reduced the grain boundary, leading to weakened defect scattering, which caused an enhancement in conductivity.