Insights into the Charge-Transfer Stabilization of Heterostructure Components with Unstable Bulk Analogs

摘要

Solid state chemists have yet to find a targeted approach based on simple rules to predict new materials with desired physical properties. Recent advances in computational high throughput methods have led to the creation of large databases with predicted new compounds. While many of these compounds are unstable, some may be stabilized inside heterostructures. BiSe is an example for such a compound where the rock-salt structure is unstable in bulk but can be found in misfit layer compounds and ferecrystals. In some of these heterostructures, BiSe also exhibits antiphase boundaries (APBs), periodic Bi-Bi pairings that interrupt the alternating pattern of the rock-salt structure. Understanding the behavior of BiSe may aid in the discovery of new heterostructure components where no stable bulk analog exists. We used density functional theory (DFT) and crystal orbital Hamilton populations (COHPs) to explain the different stabilities of rock-salt structured BiSe. COHPs show that rock-salt structured BiSe has occupied antibonding states at the Fermi level, which destabilize the structure. In heterostructures, these states can be depopulated by donating electrons into an adjacent layer or by forming APBs to localize electrons into a Bi-Bi bond. The results suggest that the depopulation of antibonding states is crucial to stabilizing rock-salt structured BiSe, and that BiSe needs to be paired with a suitable electron acceptor. We predict that this is a general principle that can be applied to other compounds with unstable polytypes and suggest that COHPs should play a larger role in the discovery of new heterostructure components.