Faculty Publications

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Author: search.filters.author.Basu, R.Subject: search.filters.subject.Germanium compounds

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    Synergistic manifestation of band and scattering engineering in the single aliovalent Sb alloyed anharmonic SnTe alloy in concurrence with rule of parsimony
    (Royal Society of Chemistry, 2021) Basu, R.; Mandava, S.; Shenoy, U.S.; Bhat, D.K.; Khasimsaheb, B.; Debnath, A.K.; Singh, A.; Neeleshwar, S.
    Several endeavors were adapted to improve the thermoelectric performance of SnTe as a substitute of toxic PbTe and the booming approaches comprise introduction of nanostructuring, resonance states, valence band convergence and interstitial or substitutional defects. In this study, a stratagem was designed to incorporate single aliovalent Sb in SnTe by a one-step approach which successfully modulates the electronic and thermal transport properties by integration of several approaches, viz. energy-filtering effect, valence band convergence and phonon scattering at all length scales synergistically. Here, the alteration of the band structure of SnTe incorporated with Sb leads to substantial improvement of the Seebeck coefficient, essentially beneficial for the performance of thermoelectric alloys, beyond the designated critical temperature at 473 K which shows the onset of strong contribution of the heavy (?) valence band. The experimental finding of band convergence by Sb was for the first time corroborated by theoretical validation by Density Functional Theory (DFT) calculations. In addition, the presence of mass fluctuation, secondary precipitates, interfaces and the long-range interactions due to resonant bonding leading to optical phonon softening, large phase space available for three-phonon scattering and strong anharmonicity enables an ultralow lattice thermal conductivity of ?0.5 W m-1 K-1. Thus, a zT value of ?0.72 at 775 K is recorded for the SnTeSb0.05 composition, which is 154% enhancement compared to our pristine SnTe and is strongly competing with numerous reported zT values using considerably less abundant Ag, Ge, In and highly toxic Pb, Hg, Bi, Cd multiple elements as either a dopant or an additive. Thus, the law of parsimony is maintained with reduction in the cost of the thermoelectric module. © The Royal Society of Chemistry.
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    Entropy engineering in I-V-VI2 family: a paradigm to bestow enhanced average ZT in the entire operating temperature regime
    (Royal Society of Chemistry, 2024) Basu, R.; Shenoy, U.S.; Pathak, A.; Singh, S.; Jha, P.; Bhat, D.K.; Basu, H.; Singh, A.
    The design and development of n-type alloys in the mid-temperature regime (500-700) K with enhanced thermoelectric performance is of utmost necessity for the fabrication of thermoelectric devices. In this regard, the I-V-VI2 family reveals superior thermoelectric performance, owing to the fact that group V elements have non-bonded electrons and high Z (atomic number), with a high Grüneisen parameter, which cause amplified anharmonicity and subsequently low intrinsic lattice thermal conductivity. However, the irony is that the well-studied alloy of this family, AgBiSe2, undergoes phase transition in the operating temperature range. Thus, of paramount importance is restricting the phase transition and bringing it down below room temperature (RT), along with stabilizing a highly symmetrical crystal structure in the extended operating temperature range. Efforts were made to synthesize a cubic n-type AgBiSeS alloy belonging to the I-V-VI2 compounds (unlike AgBiSe2) that is stabilized throughout the temperature range, as the S element aids in strengthening of the chemical bonds. In addition, the alloy was further stabilized by forming a solid solution with PbSe, which aids in increasing the configurational entropy and thereby increases the chemical space of the system. The resultant alloys possess intrinsically low lattice thermal conductivity ranging from 0.38-0.74 W m−1 K−1 in the entire operating range. Consequently, the peak ZT was reported as ∼0.6 at 780 K, with an average ZT value of 0.3 for the alloy (AgBiSeS)0.5(PbSe)0.5 within 300-823 K. Although the reported ZT is low, the methodology of entropy-driven structural stabilization in the operating temperature regime was adapted to attain a highly symmetrical, stable structure for practical applications. © 2024 RSC.