Structural, magnetic and thermoelectric properties of Delafossite-type oxide, CuCr_1-xMg_xO₂(0 ≤ × ≤ 0.05)

We report structural, magnetic and high-temperature thermoelectric properties of Delafossite-type oxide, CuCr_1-xMg_xO ₂ (0≤×0.05). Lattice parameter, c, linearly decreases with increasing Mg concentration in the range, 0≤ × <0.03. This decrease is mainly caused by the shrinking of O-Cu-O dumbbells which connect the CdI ₂-type (Cr/Mg)O₂ slabs. Magnetic susceptibility measurements indicate that Cr³⁺ is in the high spin state in the paramagnetic phase above 25 K. Electrical resistivity, ρ, of CuCr _1-xMg_xO₂ exhibits semiconducting behavior (dp/dT<0) in the range from 350 K to 1100 K and becomes lower through the partial substitution of Mg²⁺ for Cr₃₊ in 0≤×≤0.03. Due to positive Seebeck coefficients, S, of these oxides, it is natural to assume that the dominant charge carriers of CuCr _1-xMg_xO₂ are positive holes. Experimental values of Sat 1100 K have consistency with the theoretical values predicted from Koshibae's formula. From the linear S vs. lnσ plot, it is estimated that the observed power factor, S²σ, reaches the maximum value around x=0.03 in this system. The thermal conductivity, Κ, for CuCr _1-xMg_xO₂ ranges from 6 to 10 W·m _-1·K^-1 at 300 K. The maximum dimensionless figure of merit, ZT=S²T/ρΚ, of the sample with x=0.03 is 0.04 at 950 K.