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Item Resonance states and hyperconvergence induced by tungsten doping in SnTe: Multiband transport leading to a propitious thermoelectric material(Elsevier Ltd, 2022) Shenoy, U.S.; D, G.K.; Bhat, D.K.Discovery of dopants which can engineer the electronic structure of the thermoelectric materials beneficially to improve the figure of merit has been receiving a lot of attention. In this work, we study one such unique dopant, tungsten in SnTe by implementing first principles density functional theory approach. We predict that tungsten is a n-type resonant dopant which not only increases the band gap but causes convergence of valence sub-bands leading to increased Seebeck co-efficient due to increase in the effective mass and decrease in the bipolar conduction. We show for the first time, the introduction of hyperconvergence in the conduction sub-bands, a feature which was observed only in valence bands of SnTe and GeTe. In addition to the above features, it also introduces multiple electronic valleys near the Fermi level excluding the use of a co-dopant to exploit the benefits of the electronic structure engineering. A maximum ZT of ~1.61 theoretically achieved by tuning the chemical potential at 800 K makes this material worth being explored experimentally. © 2022 Elsevier B.V.Item A case of perfect convergence of light and heavy hole valence bands in SnTe: the role of Ge and Zn co-dopants(Royal Society of Chemistry, 2022) Shenoy, U.S.; D, G.K.; Bhat, D.K.A dual step approach of decreasing the thermal conductivity and improving the power factor by using two different dopants has shown great promise in the development of high performance thermoelectrics. In this work, we dope Ge, which is well known to decrease the thermal conductivity of SnTe. Later, to this, we co-dope Zn to simultaneously improve the power factor. Zn, in the presence of Ge, introduces resonance levels, thus distorting the density of states near the Fermi level, improving the room temperature performance. In addition, it is also able to increase the band gap, thus preventing bipolar diffusion at high temperatures. The unique feature exhibited is the perfect convergence of light and heavy hole valence sub-bands achieved for the first time in SnTe promising a high performance throughout the temperature range. The transport property calculations reveal that in addition to p-type, it can also act as an outstanding n-type material by tuning its chemical potential, making it worth studying experimentally. © 2022 RSC.Item Probing of Bi doped GeTe thermoelectrics leads to revelation of resonant states(Elsevier Ltd, 2022) Shenoy, U.S.; D, G.K.; Bhat, D.K.Quest for lead free high performance mid temperature thermoelectric materials has led to extensive research on SnTe and GeTe based materials. Among various strategies implemented to improve the transport properties of GeTe, electronic structure engineering holds a prominent place. Herein, we reinvestigate the impact of substitutional doping of Bi in GeTe on its electronic structure in both rhombohedral and cubic phase. We uncover that Bi introduces resonance levels in GeTe acting as a first n-type resonant dopant in both rhombohedral and cubic phases. We also report for the first time that Bi resonance states undergo Rashba splitting in low temperature rhombohedral phase. Bi doping acts in a multifunctional way by tuning the carrier concentration, causing conduction band convergence and phonon scattering in addition to improving the band effective mass by distorting the density of states near the Fermi level to enhance the thermoelectric performance of the material. The convergence of L, Z and Σ valence bands in rhombohedral phase due to Bi doping leads to manifestation of Rashba effect in p-type material which was not reported till date. Thus, we propose that the chemical potential tuning can result in p-type as well as n-type Bi doped GeTe for thermoelectric application. © 2022 Elsevier B.V.