Semiconducting BaS3 phase featuring v-shape S3 unit at high pressure

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Pressure-induced structural transformation of known compounds has become an effective routine to obtain new materials. The sulfur motifs that are present in compounds have a considerable effect on their crystal structures and electronic properties. Here, we focus on exploring the evolution of S motifs in the $\mathrm{Ba}{\mathrm{S}}_{3}$ compound under high pressure. A novel $P{3}_{1}21\text{\ensuremath{-}}\mathrm{Ba}{\mathrm{S}}_{3}$, consisting of an equivalent V-shape ${\mathrm{S}}_{3}$ unit and quasi-hexagon Ba ring, is identified through the combination of first-principles swarm-intelligence search and phonon softening calculations. The bond angle in the ${\mathrm{S}}_{3}$ unit decreases, accompanied by pressure-induced structural phase transition. $P{3}_{1}21\text{\ensuremath{-}}\mathrm{Ba}{\mathrm{S}}_{3}$ shows a semiconducting character, mainly originating from the contribution of S $3p\text{\ensuremath{-}}\mathrm{electron}$ states. Along with the newly proposed $\mathrm{Ba}{\mathrm{S}}_{3}$ structure, the temperature effect on stability is estimated using the temperature-dependent effective potential method. For another S-rich $\mathrm{Ba}{\mathrm{S}}_{2}$, the disappearance of the ${\mathrm{S}}_{2}$ unit induced by pressure ($>150\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$) is mainly responsible for structural instability.