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Complex multicomponent systems based on PbTe, SnTe, and GeTe are of greatinterest for infrared devices and high-temperature thermoelectric applications.A deeper understanding of the atomic and electronic structure of thesematerials is crucial for explaining, predicting, and optimizing theirproperties, and to suggest new materials for better performance. In this work,we present our first-principles studies of the energy bands associated withvarious monovalent (Na, K, and Ag) and trivalent (Sb and Bi) impurities andimpurity clusters in PbTe, SnTe, and GeTe using supercell models. We find thatmonovalent and trivalent impurity atoms tend to come close to one another andform impurity-rich clusters, and the electronic structure of the host materialsis strongly perturbed by the impurities. There are impurity-induced bandsassociated with the trivalent impurities that split off from theconduction-band bottom with large shifts towards the valence-band top. This isdue to the interaction between the $p$ states of the trivalent impurity cationand the divalent anion which tends to drive the systems towards metallicity.The introduction of monovalent impurities (in the presence of trivalentimpurities) significantly reduces (in PbTe and GeTe) or slightly enhances (inSnTe) the effect of the trivalent impurities. One, therefore, can tailor theband gap and band structure near the band gap (hence transport properties) bychoosing the type of impurity and its concentration or tuning themonovalent/trivalent ratio. Based on the calculated band structures, we areable to explain qualitatively the measured transport properties of the wholeclass of PbTe-, SnTe-, and GeTe-based bulk thermoelectrics.

Impurity clustering and impurity-induced bands in PbTe-, SnTe-, and GeTe-based bulk thermoelectrics