BaSn2 : A wide-gap strong topological insulator

${\mathrm{BaSn}}₂$ has been shown to form as layers of buckled stanene intercalated by barium ions. However, despite an apparently straightforward synthesis and significant interest in stanene as a topological material, ${\mathrm{BaSn}}₂$ has been left largely unexplored, and has only recently been recognized as a potential topological insulator. Belonging to neither the lead nor bismuth chalcogenide families, it would represent a unique manifestation of the topological insulating phase. Here we present a detailed investigation of ${\mathrm{BaSn}}₂$, using both ab initio and experimental methods. First-principles calculations demonstrate that this overlooked material is indeed a strong, wide-gap topological insulator with a bulk band gap of 200 meV. We characterize the surface state dependence on termination chemistry, providing guidance for experimental efforts to measure and manipulate its topological properties. Additionally, through ab initio modeling and synthesis experiments, we explore the stability and accessibility of this phase, revealing a complicated phase diagram that indicates a challenging path to obtaining single crystals.