Prediction of ternary alkaline-earth metal Sn(II) and Pb(II) chalcogenide semiconductors

Abstract

Sn(II) and Pb(II) compounds, especially chalcogenides, are important functional materials. The complementary properties of these two families of compounds, with differences related to the differences in stability of the divalent state and relativistic effects on the band structures, provide tunability of properties and also can guide searches for new phases. In particular, it suggests the existence of previously unknown ternary Sn(II) and Pb(II) chalcogenide phases. Here, we predict the existence of stable compounds via first-principles global optimization structure searches on the alkaline-earth metal Sn(II) and Pb(II) chalcogenide systems. This leads to five new stoichiometries. These unreported phases, ${\mathrm{SrSnS}}_{2}$, ${\mathrm{SrSnSe}}_{2}$, ${\mathrm{SrPbSe}}_{2}$, ${\mathrm{BaSnSe}}_{2}$, and ${\mathrm{BaPbS}}_{2}$, are thermodynamically preferred by Sn-rich (or Pb-rich) conditions, which favor the divalent state. They are semiconducting with band gaps ranging from 0.80 to 1.85 eV, strong visible light absorption and relatively light hole and electron effective masses ($l1$ ${\mathrm{m}}_{0}$). The valence band maxima of these compounds have antibonding character involving metal $s$ and chalcogen $p$ character. This is a feature that is often associated with defect tolerant behavior. In addition the compounds show complex band structures of a type that is favorable for thermoelectric performance.