Mn-Substitution Effect on Thermal Conductivity of Delafossite-Type Oxide CuFeO2

We have prepared the CuFe1-x Mn (x) O-2 solid solution to enhance the thermoelectric performance of CuFeO2 by reducing its thermal conductivity kappa. With increasing x above 0.4, the crystal structure changes from delafossite (R (3) over barm) to crednerite (C2/m). CuFe0.5Mn0.5O2 exhibits the lowest kappa value of 2.28 W/m K at the theoretical density, being about one-quarter of that of the end members, CuFeO2 and CuMnO2. We discuss the temperature dependence of kappa in terms of a classical phonon transport model, and conclude that local structural modulation due to the mixture of undistorted FeO6 octahedra and distorted MnO6 octahedra in CuFe1-x Mn (x) O-2 leads to the significant reduction of kappa.