Browsing by Author "Yi, S."

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    Optimized electronic performance in half-Heusler Ti-doped NbFeSb materials by stoichiometric tuning at the Fe and Sb sites
    (Elsevier Ltd, 2022) Kahiu, J.N.; Shenoy, U.S.; Kihoi, S.K.; Kim, H.; Yi, S.; Bhat, D.K.; Lee, H.S.
    Electronic structure is known to be highly influenced by the site occupancy and the stoichiometry of the material which in turn largely effects the thermoelectric properties. Herein, we present electronic calculations using density functional theory (DFT) of non-stoichiometric Ti doped NbFeSb configuration, showing the effect of the anti-site Fe atoms on the electronic properties, and supporting them with experimental results of the prepared Nb0.8Ti0.2Fe1+xSb1−x samples. The electronic structure of the non-stoichiometric sample shows the introduction of two distinct peaks near the Fermi level by the Fe atoms at the Sb sites. These resonance states are known to cause an increase in the density of states effective mass near the Fermi level, which explains the increase in the Seebeck coefficient in the sample x = 0.03 compared to the sample x = 0.00. In addition, a comparatively higher electrical conductivity is reported from sample x = 0.03, which is attributed to the aliovalent substitution of Sb atoms by Fe atoms. The simultaneous increase in the Seebeck coefficient and electrical conductivity culminates in an increased power factor of ∼50.3 µW/cmK2 at 373 K, which is ∼46% higher than that of samples x = 0.00 and x = 0.05, highlighting the possibility of increasing the power density by stoichiometric variation to achieve the high joule-per-dollar performance of NbFeSb-based TE devices, the relevance of which is also currently emphasized in the quest for commercial viability. © 2021 Elsevier B.V.
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    Optimized Mn and Bi co-doping in SnTe based thermoelectric material: A case of band engineering and density of states tuning
    (Chinese Society of Metals, 2021) Kihoi, S.K.; Kahiu, J.N.; Kim, H.; Shenoy, U.S.; Bhat, D.K.; Yi, S.; Lee, H.S.
    Tin telluride (SnTe) overwhelmingly continues to be studied owing to its promising thermoelectric properties, tunable electronic structure, and its potential as an alternate to toxic lead telluride (PbTe) based materials. In this research, we engineer the electronic properties of SnTe by co-doping Mn and Bi below their individual solubility limit. The First principles density functional theory studies reveal that both Bi and Mn introduce resonance states, thereby increasing the density of states near the Fermi level leading to enhanced Seebeck coefficient. This unique combination of using two resonant dopants to introduce flatter bands is effective in achieving higher performance at lower temperatures manifesting into a large Seebeck value of ?91 ?V/K at room temperature in the present case. Both elements optimally co-doped results in a very high power factor value of ?24.3 ?W/cmK2 at 773 K when compared to other high performance SnTe based materials. A zT of ?0.93 at 773 K is achieved by tuning the proportion of the co-dopants Mn and Bi in SnTe. The hardness value of pristine SnTe was also seen to increase after doping. As a result, synergistic optimized doping proves to be a suitable means for obtaining thermoelectric materials of superior characteristics without the need for heavy doping. © 2021