"Research is the bridge between curiosity and discovery—where questions become progress."
"In science, every experiment tells a story—and every result brings us closer to understanding the world."
My research lies at the intersection of materials design, transport phenomena, and thermoelectric energy conversion, with a particular focus on understanding and improving the performance of thermoelectric materials for waste heat recovery. I combine hands-on experimental work with first-principles simulations, aiming to create a closed-loop discovery platform for emerging thermoelectric materials. Below is an overview of my key research areas.
1. Instrumentation:
A significant part of my Ph.D. research at IIT Mandi was dedicated to the design and fabrication of a custom high-temperature thermoelectric measurement setup. The instrument enables the simultaneous measurement of the Seebeck coefficient and thermal conductivity of bulk materials in the temperature range of room temperature up to 800 K. This setup was critical for characterizing a wide range of thermoelectric materials with high reliability, reproducibility, and cost efficiency. The device was calibrated using standard reference materials and provided the foundation for multiple experimental studies throughout my doctoral work.
2. Characterization and Measurements:
My experimental research focuses on the synthesis and characterization of thermoelectric materials, using techniques such as solid-state reaction, chemical routes, arc melting, and spark plasma sintering (SPS). I specialize in high-temperature transport measurements and structural/microstructural analysis. My work spans a variety of material systems, integrating both experimental and computational approaches:
Fe₂VAl: We explored the TE properties of Fe₂VAl at high temperatures, employing five different XC functionals (LDA, PBE, mBJ, PBEsol, and SCAN) to evaluate the Seebeck coefficient (S). The best agreement between experimental and theoretical results was achieved by setting the mBJ band gap with the band structure obtained from PBEsol or SCAN. To gain further insights into the experimentally observed TE parameters, we used DFT-based semi-classical Boltzmann transport theory, which revealed that multi-band electron and hole pockets significantly influenced transport trends. The phonon dispersion of Fe₂VAl was computed using the finite displacement method and supercell approach implemented in the Phonopy code, confirming the mechanical stability of the compound. Thermal expansion calculations were performed under the quasi-harmonic approximation, while κL was determined using first-principles anharmonic lattice dynamics calculations with the Phono3py code. Additionally, forces on individual atoms were computed using the projector augmented wave (PAW) method within Abinit. The theoretical κL values were compared with experimental data, demonstrating good agreement and validating the computational approach.
Na₀.₇₄CoO₂: We used a combined experimental and computational approach to examine the TE properties of Na₀.₇₄CoO₂. Electronic structure calculations were performed using the full-potential linearized augmented plane wave (FP-LAPW) method implemented in WIEN2k code. The structure was optimized through force minimization in self-consistent DFT calculations. Transport properties were then computed using the BolzTraP package based on Boltzmann semi-classical transport theory. The best agreement between experimental and theoretical results was achieved through spin-polarized DFT+U calculations with U = 4 eV. Our computational studies further suggested the potential for n-type conduction in Na 0.74CoO2, which could lead to a figure of merit (zT) exceeding 2 at high temperatures.
CoSi: In our research on topological semimetal CoSi, we investigated the influence of exchange-correlation (XC) functionals and the role of 3s(2p) orbitals of Co(Si) as core/valence states on its vibrational and thermal properties. The experimentally observed TE properties of CoSi were analyzed using DFT-based Boltzmann transport theory, incorporating spin-orbit coupling effects. Multi-band electron and hole pockets were found to play a key role in determining the temperature-dependent transport behavior. The temperature-dependent relaxation time (τ) was obtained by comparing experimental electrical conductivity (σ) with theoretical σ/τ, which were further used to compute the electronic component of thermal conductivity (κₑ). The computed values of κₑ, and lattice thermal conductivity (κL). The computed κL at 300 K showed good agreement with experimental data. Additionally, thermal expansion calculations based on DFT provided reliable estimates consistent with experimental results.
Marcasite-type MSb₂ (M = Ta, Nb): We investigated the thermoelectric properties of marcasite-type compounds MSb₂ (M = Ta, Nb) in the intermediate temperature range. The materials were synthesized using solid-state reaction followed by spark plasma sintering and confirmed to crystallize in a monoclinic C2/m phase. Seebeck coefficient measurements indicate n-type behavior with a non-monotonic temperature dependence. Both electrical and thermal conductivities increase with temperature. First-principles DFT combined with Boltzmann transport theory explains the observed semimetallic behavior, characterized by a pseudogap near the Fermi level and multi-band conduction. Theoretical predictions show good agreement with experimental trends, suggesting moderate thermoelectric performance for both compounds.
Characterization tools I work with include:
X-ray diffraction and Rietveld refinement
Scanning electron microscopy
Four-probe resistivity measurement setup in the high temperature region
ZEM-3 for Seebeck coefficient and resistivity measurements
LFA-467 Hyper flash for thermal diffusivity measurement
Spark plasma sintering (SPS) for rapid densification of samples
3. Computational Approaches:
In parallel with experimental work, I utilize first-principles calculations and semi-classical transport theory to gain predictive insights into the electronic and thermal properties of thermoelectric materials.
My computational toolkit includes:
Density Functional Theory (DFT) using WIEN2k, Quantum ESPRESSO, Abinit and Elk for structural relaxation, total energy, electronic band structure, and density of states calculations.
Lattice dynamics using Phonopy, and Phono3py.
Boltzmann transport calculations using BoltzTraP and BoltzTraP2 package to compute temperature-dependent transport coefficients based on DFT-derived band structures.
Analysis of effective masses, band convergence, and density-of-states features, which are critical parameters for optimizing thermoelectric performance.
These simulations are instrumental in guiding experimental synthesis----helping to select promising dopants, identify beneficial structural motifs, and understand carrier dynamics.