Structure Matters: Expanding the Origin of the Insulator-metal Transition in BaCo1-xNixS2
We find that structural distortions play a pivotal role in the insulator-to-metal transition (IMT), in BaCo1-xNixS2despite the average structure remaining unchanged. We demonstrated that the Jahn-Teller (JT) effect, stemming from degenerate dxzand dyz orbitals sharing a single electron, is consistent with anomalous sulfide displacements observed in X-ray diffraction studies. The sulfide displacements, which relieve the JT instability, assist the opening of a band gap which exists at low Ni concentrations. Adding Ni to the system introduces extra electrons which suppress this JT effect, therefore assisting the IMT observed near 21% Ni. Since IMTs are often driven cooperatively by structural, electronic, and magnetic interactions, understanding the contributions and interplay of these degrees of freedom is crucial to designing materials with desirable properties. Knowing that lattice distortions can play a role in structure-preserving IMTs enables us to functionalize such materials for use in emerging technologies.