ABSTRACT
Oxides are of interest for thermoelectrics due to their high thermal stability, chemical inertness, low cost, and eco-friendly constituting elements. Here, adopting a unique synthesis route via chemical co-precipitation at strongly alkaline conditions, one of the highest thermoelectric performances for ZnO ceramics ( P F max = $PF_{\text{max}} =$ 21.5 µW cm-1 K-2 and z T max = $zT_{\text{max}} =$ 0.5 at 1100 K in Zn 0.96 Al 0.04 O ${\rm Zn}_{0.96} {\rm Al}_{0.04}{\rm O}$ ) is achieved. These results are linked to a distinct modification of the electronic structure: charge carriers become trapped at the edge of the conduction band due to Anderson localization, evidenced by an anomalously low carrier mobility, and characteristic temperature and doping dependencies of charge transport. The bi-dimensional optimization of doping and carrier localization enable a simultaneous improvement of the Seebeck coefficient and electrical conductivity, opening a novel pathway to advance ZnO thermoelectrics.
ABSTRACT
Thermoelectric materials seamlessly convert thermal into electrical energy, making them promising for power generation and cooling applications. Although historically the thermoelectric effect was first discovered in metals, state-of-the-art research focuses on semiconductors. Here, we discover unprecedented thermoelectric performance in metals and realize ultrahigh power factors up to 34 mW m-1 K-2 in binary NixAu1-x alloys, more than twice larger than in any bulk material above room temperature, reaching zTmax â¼ 0.5. In metallic NixAu1-x alloys, large Seebeck coefficients originate from electron-hole selective scattering of Au s electrons into more localized Ni d states. This intrinsic energy filtering effect owing to the unique band structure yields a strongly energy-dependent carrier mobility. While the metastable nature of the Ni-Au system as well as the high cost of Au pose some constraints for practical applications, our work challenges the common belief that good metals are bad thermoelectrics and presents an auspicious route toward high thermoelectric performance exploiting interband scattering.
ABSTRACT
Discovered more than 200 years ago in 1821, thermoelectricity is nowadays of global interest as it enables direct interconversion of thermal and electrical energy via the Seebeck/Peltier effect. In their seminal work, Mahan and Sofo mathematically derived the conditions for 'the best thermoelectric'-a delta-distribution-shaped electronic transport function, where charge carriers contribute to transport only in an infinitely narrow energy interval. So far, however, only approximations to this concept were expected to exist in nature. Here, we propose the Anderson transition in a narrow impurity band as a physical realisation of this seemingly unrealisable scenario. An innovative approach of continuous disorder tuning allows us to drive the Anderson transition within a single sample: variable amounts of antisite defects are introduced in a controlled fashion by thermal quenching from high temperatures. Consequently, we obtain a significant enhancement and dramatic change of the thermoelectric properties from p-type to n-type in stoichiometric Fe2VAl, which we assign to a narrow region of delocalised electrons in the energy spectrum near the Fermi energy. Based on our electronic transport and magnetisation experiments, supported by Monte-Carlo and density functional theory calculations, we present a novel strategy to enhance the performance of thermoelectric materials.
