Understanding the Thermodynamic Stability of the [100] Surface Systems of the Photovoltaic Chalcogenide Perovskite BaZrS₃

The chalcogenide perovskite material BaZrS₃ has recently been explored for various electronic applications, such as photovoltaics and thermoelectrics. Various synthetic routes employed in achieving high quality crystals have focused mainly on the bulk material using solid state synthesis with few groups employing gaseous intermediates. On the basis of application of these materials for photovoltaics and thermoelectrics, thin film synthesis routes become relevant, and the structure of the various low index surfaces is of relevance. In this study, atomistic thermodynamic modeling combined with first-principles ab initio studies is used to explore the [100] surface system. Several terminations, including reconstructions, were explored, and the most stable surfaces characterized by the surface grand potential were combined with various sulfides of Barium and Zirconium to build a practical phase diagram for the BaZrS₃ system. The constructed phase diagram can aid in synthesizing stable high quality BaZrS₃ thin films through selection of appropriate temperature and pressure regimes. We identified the (001) BaS and (001) ZrS₂ terminations as the most stable and predominant surfaces. Additionally, we identified a new stable reconstructed (100) S₄ surface obtained by substituting surface Ba atoms with Zr atoms. This surface competes strongly with the (001) ZrS₂ surface in practically accessible Zr and S chemical potential regimes.