Abstract
The solid solution exhibits an insulator-to-metal transition close to . Questions of whether this transition is coupled with structural changes remain open. Here we follow the structural evolution as a function of the Ni content using synchrotron powder x-ray diffraction and pair distribution function analyses to reveal significant basal sulfide anion displacements occurring preferentially along the pyramidal edges comprising the edge-connected bond network in . These displacements decrease in magnitude as increases and are nearly quenched in . Density-functional-theory-based electronic structure calculations on suggest that these displacements arise as a dynamic first-order Jahn-Teller effect owing to partial occupancy of nominally degenerate and orbitals, leading to local structural symmetry breaking in the -plane of the Co-rich phases. The Jahn-Teller instability is associated with the opening of a band gap that is further strengthened by electronic correlation. The Jahn-Teller effect is reduced upon increased electron filling as , indicating that the local structure and band filling cooperatively result in the observed insulator-to-metal transition.
3 More- Received 14 July 2020
- Accepted 14 September 2020
DOI:https://doi.org/10.1103/PhysRevMaterials.4.104401
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