Research interest
Thermoelectrics
A Thermoelectric(TE) material can convert heat energy into electricity and vice versa. Since huge amount of heat energy is being released into the environment during various processes (industrial furnaces/chimneys, car exhaust etc.), it is desirable to use TE devices to scavenge the waste heat and turn it into clean energy. However, their low conversion efficiency makes TEs economically nonviable. This efficiency is measured in terms of a dimensionless quantity called the TE figure-of-merit, ZT, where T stands for temperature, and Z is given by: 𝑍 = 𝜎𝑆2⁄𝜅 where 𝜎 and 𝜅 are the electrical and thermal conductivities, and S is the thermopower. TEs with ZT > 2 can enhance the power generation efficiency by 10 % to 15 %. Therefore, it is crucial to discover new TE materials with high ZT. The intermetallic Half-Heusler (HH) alloys (chemical formula: XYZ) are promising materials in this regard. Though traditionally studied for spintronics, recently they have attracted considerable attention for topological and thermoelectric properties.
NASA has been using Radioisotope Thermoelectric Generators (RTGs) for decades. They use radioactive plutonium oxide as a fuel (heat source) and power their deep space probes by converting heat into electricity using thermoelectric material.
High Entropy Alloys as Thermoelectrics:
The high-entropy concept has emerged as a powerful materials-design paradigm for stabilizing single-phase solid solutions at elevated temperatures through a large configurational entropy. By reducing the Gibbs free energy, high entropy suppresses phase segregation and promotes the formation of thermodynamically stable crystalline structures that are often inaccessible in conventional alloys. In thermoelectric materials, the resulting chemical complexity and severe lattice distortion generate strong mass and strain-field fluctuations, which effectively scatter heat-carrying phonons and significantly reduce lattice thermal conductivity.
This reduction in thermal transport, when achieved without substantial degradation of electronic properties, can lead to enhanced thermoelectric performance and higher zT values. In our work on the entropy-stabilized half-Heusler alloy (TiHf)₁/₂(FeCoNi)₁/₃Sb, high-entropy alloying enabled the formation of a stable single-phase structure with pronounced lattice disorder, resulting in an ultralow lattice thermal conductivity approaching the amorphous limit. The combination of entropy stabilization and strong phonon scattering demonstrates the potential of high-entropy engineering as an effective route for developing next-generation high-performance thermoelectric materials.
Defect Engineering:
Defect engineering has emerged as a powerful strategy for enhancing the thermoelectric figure of merit (zT) by simultaneously tuning electronic and phononic transport. Beyond conventional carrier concentration optimization, controlled introduction of point defects, vacancies, and antisite disorder can modify the electronic band structure, increase the density-of-states effective mass, and strengthen phonon scattering. In Ti-substituted TaFeSb, enhanced antisite disorder induced by Fe deficiency was found to increase the Seebeck effective mass while suppressing lattice thermal conductivity, resulting in a substantial improvement in zT. The highest zT of 1.55 was achieved in highly disordered arc-melted samples, demonstrating that carefully engineered defect landscapes can create a favorable balance between electrical transport and thermal resistance. These results highlight defect engineering as an effective route for realizing high-performance thermoelectric materials beyond the limits of traditional carrier optimization.
Transport Calculation methods ...
Hybrid energy device