Ady's work on using inertial effective mass as descriptor in the screening of potential TE materials

Effective mass has been touted as an important descriptor in thermoelectric transport. Based on theoretical intuition, some reports demonstrate that low effective mass is preferable in thermoelectrics, while others propose that a large density of states effective mass for high Seebeck is the pathway to better thermoelectric materials. Leveraging on the available data from Materials Project, we present a data-driven conclusion that corroborates the central role of effective mass in high-throughput thermoelectric materials screening. The efficacy of the Fermi surface complexity factor in enhancing power factor is analyzed in relation to the effective mass for a large number of compounds. Here, we show that starting with a low inertial effective mass material, any changes in Fermi surface complexity factor will have a pronounced effect on its thermoelectric power factor and verify this strategy in recently discovered thermoelectric materials. This can be accomplished by employing band engineering using doping, or symmetry distortion, and starting with a base material that intrinsically possesses a low inertial effective mass.

Hong Kuan's work on lithium-intercalated molybdenum disulfide (LixMoS2)

Layered transition metal dichalcogenides (TMDCs) intercalated with alkali metals exhibit mixed metallic and semiconducting phases with variable fractions. Thermoelectric properties of such mixed-phase structure are of great interest because of the potential energy filtering effect, wherein interfacial energy barriers strongly scatter cold carriers rather than hot carriers, leading to enhanced Seebeck coefficient (S). Here, we study the thermoelectric properties of mixed-phase LixMoS2 as a function of its phase composition tuned by in situ thermally driven deintercalation. We find that the sign of Seebeck coefficient changes from positive to negative during initial reduction of the 1T/1T′ phase fraction, indicating crossover from p- to n-type carrier conduction. These anomalous changes in Seebeck coefficient, which cannot be simply explained by the effect of deintercalation-induced reduction in carrier density, can be attributed to the hybrid electronic property of the mixed-phase LixMoS2. Our work shows that careful phase engineering is a promising route toward achieving thermoelectric performance in TMDCs.

Editor's Pick in RSI: Pawan and Maheswar's shadow mask technique to measure thin film Seebe

Organics, hybrid (inorganic-organic), PLD, MBE, sputtering, evaporation - you name it! No matter how you make your films, we can measure the transport properties including Seebeck, four-probe electrical conductivity and Hall to characterize your film! Pawan and Maheswar calibrated the technique with PEDOT:PSS as well as Nickel and we are now routinely using this in our lab for measurements on organic, hybrid, semiconducting films with <1% error bars! Anas and Wu Jing are now working on the AC version of this technique - should be greatly useful for smaller size samples... Congratulations folks!