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

Khang Hoang
Materials Department, University of California, Santa Barbara, California 93106, USA

S. D. Mahanti
Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA

Mercouri G. Kanatzidis
Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA
Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA

Abstract

Complex multicomponent systems based on PbTe, SnTe, and GeTe are of great interest for infrared devices and high-temperature thermoelectric applications. A deeper understanding of the atomic and electronic structure of these materials is crucial for explaining, predicting, and optimizing their properties, and to suggest new materials for better performance. In this work, we present our first-principles studies of the energy bands associated with various monovalent (Na, K, Ag) and trivalent (Sb, Bi) impurities and impurity clusters in PbTe, SnTe, and GeTe using supercell models. We find that monovalent and trivalent impurity atoms tend to come close to one another and form impurity-rich clusters, and the electronic structure of the host materials is strongly perturbed by the impurities. There are impurity-induced bands associated with the trivalent impurities that split off from the conduction-band bottom with large shifts towards the valence-band top. This is due to strong hybridization between the p states of the trivalent impurity cations (Sb, Bi) and the divalent anion (Te) which tends to drive the systems towards metallicity. The introduction of the monovalent impurities (in the presence of the trivalent impurities) to PbTe, SnTe, and GeTe significantly reduces (in PbTe and GeTe) or slightly enhances (in SnTe) the effect of the trivalent impurities. One, therefore, can tailor the band gap and band structure near the band gap (hence transport properties) by choosing the type of impurity and its concentration or tuning the monovalent/trivalent ratio. Based on the calculated band structures, we are able to explain qualitatively the measured transport properties of the whole class of PbTe-, SnTe-, and GeTe-based bulk thermoelectrics.



References


All of the above information has been extracted automatically from the TeX source file. No human has checked this output. Due to the complications involved, there may well be inaccuracies in the title, authors, abstract, references, and links. Links may be broken for a variety of reasons; the ADS records are known to be incomplete. The reference section shown has been modified from the original text for formatting and interpretation reasons. Some reference sections are not formatted well enough to process properly. The program tries to split multiple references. Occasionally, the numbers of the references are offset by a small number. There is no need to report such technical problems to the APS. Links to APS journals go either to the archive (PROLA) or to the current contents. Links to ADS and Google are courtesy of NASA's Astrophysics Data System and Google, respectively. Abstracts and references are available for free but users may require a subscription (individual or institutional) to access the full text.