Structural, magnetic and thermoelectric properties of Delafossite-type oxide, CuCr1-xMgxO2(0⩽x⩽0.05)

We report structural, magnetic and high-temperature thermoelectric properties of Delafossite-type oxide, CuCr
_1-x
Mg
_x
O
₂
(0⩽ x ⩽0.05). Lattice parameter, c, linearly decreases with increasing Mg concentration in the range, 0⩽ x ⩽ 0.03. This decrease is mainly caused by the shrinking of O-Cu-O dumbbells which connect the CdI
₂
-type (Cr/Mg)O
₂
slabs. Magnetic susceptibility measurements indicate that Cr
³⁺
is in the high spin state in the paramagnetic phase above 25 K. Electrical resistivity, ρ, of CuCr
_1-x
Mg
_x
O
₂
exhibits semiconducting behavior (dρ/dT < 0) in the range from 350 K to 1100 K and becomes lower through the partial substitution of Mg
²⁺
for Cr
³⁺
in 0 ⩽ x ⩽ 0.03. Due to positive Seebeck coefficients, S, of these oxides, it is natural to assume that the dominant charge carriers of CuCr
_1-x
Mg
_x
O
₂
are positive holes. Experimental values of S at 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, S
²
σ, reaches the maximum value around x = 0.03 in this system. The thermal conductivity, κ, for CuCr
_1-x
Mg
_x
O
₂
ranges from 6 to 10 W·m
^-1
·
^-1
at 300 K. The maximum dimensionless figure of merit, ZT = S
²
T/ρκ, of the sample with x = 0.03 is 0.04 at 950 K