Decoupling Electronic and Thermal Transport in Spinel Oxide

Decoupling electronic and thermal transport properties remains the biggest challenge in finding efficient thermoelectric materials. We demonstrate an approach to decoupling the complex interdependence among electrical conductivity, Seebeck coefficient, and lattice thermal conductivity in spinel oxides. Utilizing the effects of tetrahedral and octahedral coordination on bonding characteristics, we demonstrate tuning the electronic and thermal transport properties of cobalt-based spinel oxides ACo₂O₄. Tetrahedrally coordinated cation A (Zn/Cd) controls the electronic transport, while thermal transport has been controlled by octahedrally coordinated cation B (Co). The combination of heavy bands and contribution of the tetrahedrally coordinated environment of Co near valence band maxima (VBM) and conduction band minima (CBM) results in an enhanced power factor. Additionally, the substitution of Cd for Zn on an octahedrally coordinated cation site leads to one order of magnitude reduction in the lattice thermal conductivity (κ_l). This reduction is attributed to the significant mass difference, phonon modes, phonon lifetime, and remarkably strong anharmonic scattering introduced by Cd. Simultaneously achieved high power factor and low lattice thermal conductivity resulting in an enhanced figure of merit value of 1.68 for Cd-spinel. The approach of decoupling atomic contributions utilizing various cationic sites demonstrates a potential route to enhance thermoelectric performance.