Thermoelectric Properties of Delafossite CuCr_1-xFe_xO₂ (0 ≤ x ≤ 1)

Understanding the different conduction mechanisms in electrical and thermal conductivity is the central key point for improving the thermoelectric property of a material. Besides, the typical parameters like carrier concentration, lower thermal conductivity for good thermoelectric materials, the effect of phonon/magnon drag, spin Seebeck effect, spin fluctuations can also be used as control parameters to improved thermoelectricity. It is known from literature that CuCrO₂ has large Seebeck value of around 350 µV/K at room temperature [1]. With this knowledge in background, we attempt a systematic study of electrical, thermal conductivity, heat capacity and Seebeck coefficient of CuCr_1-xFe_xO₂ (0 ≤ x ≤ 1) series. Our results exhibit sufficiently large and complex Seebeck coefficient in 20 K ≤ T ≤ 380 K. The electrical conductivity reveals p-type semiconducting nature confirmed from Hall-effect measurement and Seebeck coefficient. At low temperature, the electrical conduction mechanism obeys 3D-variable range hopping and at temperature above 150 K, thermally activated Arrhenius nature is observed. Unlike, nonmagnetic Cu-based Delafossite, thermal conductivity is strongly affected by spin-phonon scattering in CuCr_1-xFe_xO₂ compositions. Heat capacity measurements were used to identify the Debye temperature (θ_D) for all the compositions. The data confirm short and long-range magnetic ordering temperatures near the transition temperature. Out of the different processes that contribute to the total Seebeck coefficient of these compositions, our results suggest the dominance of the phonon drag effect in enhancing the observed values in Cr-rich compositions.