Experimental Materials Science
Thermoelectrics for power generation
High Entropy Materials
Composite Materials
Flexible Materials
Low temperature electronic and thermal transport
Bulk Magnetism
Resistive switching
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I work in the area of experimental materials science where I focus on the development of efficient thermoelectric materials including oxides, polymers and chalcogenides, high-entropy and entropy-stabilized oxides and exploring their correlated functional properties.
Thermoelectricity has been a very rich area of interest due to its conversion of waste heat into useful electric power. Depleting fossil fuel sources and the wastage of energy into heat in these sources have encouraged worldwide research communities in searching for the best thermoelectric (TE) materials as an alternative source of energy conversion. We aim to investigate TE materials with a high average figure-of-merit over a wide temperature range to convert waste heat into useful electric power. The following development has been made:
A. Thermoelectric Properties of Oxide Systems:
Cobalt-based oxides are potential candidates for thermoelectric applications owing to the existence of various charge states along with the spin states of cobalt. TE parameters like the Seebeck coefficient, and electrical conductivity can be tuned by changing the charge and spin states of cobalt.
We demonstrate an improvement in the figure-of-merit for Sr and Mn co-substituted LaCoO3 [https://doi.org/10.1016/j.jallcom.2017.11.334].
The TE properties in lanthanum cobalt oxide-based composite have also been investigated. An improvement in the average figure of merit has been demonstrated [https://doi.org/10.1016/j.jallcom.2018.03.347, https://doi.org/10.1088/2053-1591/aade73, http:doi.org/10.1016/j.matchemphys.2021.124750].
We demonstrated a colossal Seebeck coefficient and low thermal conductivity at room temperature in natural superlattice Aurivillius phase-perovskite composite, which is found to be promising for room temperature thermopile application [J. Alloys & Compd 853 (2018) 157001, https://doi.org/10.1016/j.jallcom.2020.157001].
A significant reduction in the thermal conductivity of the Aurivillius phase-perovskite composite has been achieved using the correlation between the interface thermal resistance and the Kapitza radius [https://doi.org/10.1016/j.jeurceramsoc.2020.08.069].
A significantly high figure of merit ~0.20 @ 463K is obtained in (1-x)La0.95Sr0.05Co0.95Mn0.05O3/(x)WC composite using the correlation between interface thermal resistance and Kapitza radius for reduced thermal conductivity. [https://doi.org/10.1016/j.jeurceramsoc.2022.03.062 ].
Magnetic field tunability of TE properties in Sr-Mn co-substituted lanthanum cobaltate is also explored. A maximum magnetothermopower of ~55% is obtained along with magnetothermal conductivity and magnetoresistance for Sr and Mn substituted LaCoO3 system[https://doi.org/10.1088/2053-1591/aad44c ].
B. Thermoelectric Properties in Chalcogenide Systems:
There are several chalcogenide systems that show promising zT values at room temperature and at high temperature, however, further improvement in average zT over a wide temperature range is required to improve the efficiency and reliability of TE applications.
We aim to improve the average zT value in chalcogenide-based systems based on the attuned electronic structure-mismatch phonon structure (AES-MPS) concept. The possibility of lower phonon thermal conductivity in composite systems based on mismatched phonon structure is shown in our recent studies [https://doi.org/10.1016/j.jeurceramsoc.2020.08.069, https://doi.org/10.1039/D0DT03752D].
The role of reduced Fermi energy and electrical contact resistance in PbTe-CoSb3 composite is investigated in detail [https://doi.org/10.1016/j.jeurceramsoc.2022.01.049].
Engineering electronic structure (Fermi level optimization, band convergence) and lattice dynamics (phonon group velocity, point defect scattering) result in an enhanced figure of merit in Mn-Sb co-doped GeTe [http://doi.org/10.1021/acs.chemmater.1c00331, https://10.1103/PhysRevMaterials.7.045402 ].
The understanding of the origin of electrical contact resistance and interface thermal resistance further led to improve the average zT and hence efficiency in GeTe/WC composite [https://doi.org/10.1021/acsami.2c11369 ] and LSCMO/WC composite [https://doi.org/10.1016/j.jeurceramsoc.2022.03.062].
Boosting Thermoelectric Performance in Nanocrystalline Ternary Skutterudite (Co-(Ge1.22Sb0.22)Te1.58 ) Thin Films through Metallic CoTe2 Integration [https://doi.org/10.1021/acsami.3c17695]
C. Exploring New High Entropy Oxides:
High entropy oxides (HEOx) constitute a new “class” of materials, discovered in 2015, where Rost et al extended the concept of high entropy alloys to ionically bonded ceramics. HEOx are made up of at least 5 cations populated at single crystallograhpic site to increase the configurational entropy which dominates the thermodynamic stability at high temperature. The evolution of the mixture is then no longer controlled by the enthalpy of formation, and the system crystallizes in a metastable solid solution, which can be frozen at ambient temperature by quenching, forming a material stabilized by entropy. The oxides obtained do not constitute “classical” solid solutions, but solid solutions stabilized by entropy, which makes it difficult to predict their properties, which are not just a combination of those of the starting oxides.
In this view, after discovery of entropy-stabilized rock-salt structured oxides, we have synthesized first entropy-stabilized fluorite oxides which has been found to be suitable for multifunctional properties such as thermal barrier coating, photocatalysis etc. (10.1039/D3TA02124F)
High entropy rare-earth manganites show peculiar magnetic and electrical properties as compared to simple rare-earth manganites. (https://doi.org/10.1016/j.mtphys.2023.101026)
We have demonstrated a record high zT in polycrystalline oxide materials (zT~0.23 @ 350K) in high-entropy rare-earth cobaltates where the random distribution of several cations at single-crystallographic site results in a significant reduction in lattice thermal conductivity, thereby enhancing zT. [https://doi.org/10.1016/j.jmat.2022.08.001]
New High Entropy Wolframite Oxide shows reduced thermal conductivity due to large lattice disorder. [https://doi.org/10.1002/pssr.202300372]
D. Flexible Thermoelectrics: Room temperature flexible TE systems for wearable and portable electronic devices using inorganic and organic materials is an interesting research area. In flexible TE systems, along with high zT values, the flexibility of the materials is also required.
We report an improvement in the zT for inorganic-organic composites along with enhanced flexibility [https://doi.org/10.1088/2053-1591/ab43a7, http://doi/org/10.1016/j.physb.2020.412275].
E. Coupling of Resistive switching and Thermoelectric Properties: We demonstrate the coupling between the resistive switching and thermoelectric phenomenon for the first time in LaCoO3/Graphene bulk composite system [https://doi.org/10.1063/5.0009666].
F. Realizing the TE materials in a module: We have developed different p- and n-type TE materials which we are using to prepare physical modules for practical applications.
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