A group of researchers from the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR) has worked with the quantum material TlBiSe2 to investigate its advanced functional properties.
Thermoelectric materials have drawn significant attention as they demonstrate direct and reversible conversion between electrical and thermal gradients, offering prospects for sustainable energy. A group of researchers from the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR) in Bengaluru has worked with TlBiSe2, a quantum material, to investigate advanced functional properties in them.
The performance of a thermoelectric material is evaluated based on a dimensionless figure of merit (FOM) called zT. The higher the zT, the higher the efficiency. Increasing zT is, however highly challenging due to the contradicting interdependences between the material constants that constitute zT, like the electrical and thermal conductivity, and Seebeck coefficient.
Optimization of zT requires a material that conducts electricity like a metal, conducts heat like a glass, and exhibits thermopower like a semiconductor, informs Prof. Kanishka Biswas, the lead researcher.
“To realize this seemingly impossible goal, as chemists, we turned to the biggest tool in our kit- the chemical bonding in a solid. What we needed is a chemical bond that has properties of both the bonding present in metals (for good electrical conductivity) as well as those found in glasses (for low thermal conductivity),” Prof. Biswas explains.
Quantum materials such as topological insulators, due to their unique electronic band, show very high carrier mobility harboring intriguing electrical transport. This material class shares many design features with thermoelectric materials, like heavy atoms, low band gap, spin-orbit coupling etc. Due to the shared chemical design pool, topological materials are also potential thermoelectric materials.
“TlBiSe2 demonstrates metavalent bonding. The distorted structures have energies very close to that of the undistorted structure of TlBiSe2, that at room temperature the compound can easily shuttle between the various energetically accessible configurations. TlBiSe2 showed a zT of ~0.8, the highest reported to date, amongst n-type thallium chalcogenides,” the researchers inform India Science Wire.
The study provides fundamental insights into how chemical bonding can be used to optimize thermoelectric performance in quantum material and how, by rational chemical designing, intriguing emergent properties can be realized in quantum materials to meet our ever-growing demand for advanced functional properties.
Besides Prof Kanishka Biswas, the team comprises Ivy Maria (the first author), Raagya Arora, Moinak Dutta, Subhajit Roychowdhury, and Umesh V. Waghmare. The work has been published in the Journal of American Chemical Society. The study has been supported by the Swarna-Jayanti fellowship grant, the Science and Engineering Research Board (SERB), the Department of Science & Technology (DST), India, and the Sheikh Saqr laboratory.