In our group, we perform design, modeling and atomistic simulation of materials for energy conversion and storage. These models are mostly based on first-principles density functional theory (DFT) calculations and quantum and statistical mechanics tools. Our interest is mostly in the electrical and thermal transport properties of materials. We also develop computational tools to perform and analyze simulation results in an accurate and efficient manner.
Distortions in high-entropy alloys:
Due to the mismatch between atomic size of transition metal elements, the atomic structure of the rocksalt alloy gets distorted. The distortion increases with temperature, but one can control the amount of distortion by adjusting the concentration of the alloy.
Engineering electronic properties of semimetals:
Semimetals have no bandgap and thus do not require doping to have a large electrical conductivity. Therefore any asymmetry between their electron and hole bands can result in a large thermopower without lowering of the mobility. Semimetals can thus have a large power factor. Na2AgSb is one such example.
Design and modeling of thermoelectric and thermomagnetic properties of materials from first-principles:
We have developed a methodology and related codes to compute thermoelectric and thermomagnetic properties of bulk materials. The Nernst coefficient is the transverse voltage response to a longitudinally applied thermperature gradient under a perpendicular magnetic field. If both electron and hole arriers are present in the system, and there is symmetry betwen their bands, this response can be large and competitive with the Seebeck coefficient.
Effect of strain on tranport properties of 2D materials:
We have looked at the transport properties of 2D layered materials with van der Waals interactions, and showed that a tensile strain can enlarge the gap and thus enhance the Seebeck coefficient. In the case of semimetals, one can have a metal to insulator transition with exponentially large changes in the electrical and thermal conductivities.
Novel thermionic devices:
We have designed solid-state thermionic devices based on WSe2-MoSe2 with theoretical efficiencies 19% or Carnot at room temperature and 30% of Carnot at 450K. Due to weak interlayer van der Waals interations, the cross-plane thermal conductance can be made very small and beneficial for thermionic performance.