Unexpected Semimetallic BiS₂ at High Pressure and High Temperature

In the past decade, the group V-VI compounds have been widely investigated due to their excellent properties and applications. It is now accepted that diverse stoichiometry can yield new compounds with unanticipated properties, uncovering potentially new physicochemical mechanisms. However, in this group, aside from the conventional A₂B₃-type, no other energetically stable stoichiometry has been reported yet. Here, we report that Bi₂S₃ is unstable and decomposes into stoichiometric BiS₂ and BiS with different Bi valence states upon compression. Encouragingly, we successfully synthesized the predicted BiS₂ phase and thus, confirmed its existence. Our current calculations reveal that the found BiS₂ phase is a semimetal, associated with the increased concentration of nonmetallic S. The present results represent the first counterintuitive stable stoichiometry of group V-VI and provide a good example in designing and synthesizing new compounds under compression.