2025-09-30 バッファロー大学（UB）
A University at Buffalo study provides new insights about core electrons, including their role in the B1-B2 transition that sees a compound’s atomic crystal structure rearrange from the one seen in sodium chloride (pictured) to one seen in cesium chloride.
＜関連情報＞
- https://www.buffalo.edu/news/releases/2025/09/core-electron-bonding-may-not-always-require-extreme-pressure.html
- https://pubs.acs.org/doi/10.1021/jacs.5c08582
アルカリ金属における半核電子の活性化と圧力下におけるB1-B2相転移におけるその役割 Activation of Semicore Electrons in Alkali Metals and Their Role in the B1–B2 Phase Transition under Pressure
Stefano Racioppi,and Eva Zurek
Journal of the American Chemical Society Published: August 25, 2025
DOI:https://doi.org/10.1021/jacs.5c08582
Abstract
Alkali fluorides are often thought of as archetypical ionic compounds whose structures can be understood in terms of the packing of rigid spheres. At ambient pressure, they assume the rocksalt (B1) structure, while under only a few GPa of pressure, the cesium chloride (B2) structure, with higher coordination numbers, is assumed for KF, RbF, and CsF. NaF requires almost 10 times more pressure to undergo this same phase transition, which has not been observed for LiF. Herein, we provide a detailed analysis, based upon quantum chemical calculations, explaining this behavior. We show that for the heavier alkali metals, the semicore p orbitals engage in metal–metal bonding in the B2 phase, facilitating the pressure-induced B1 → B2 structural transition. These findings suggest that the semicore orbitals of heavy alkali metals can be activated without the need of strong oxidants at very mild levels of compression, resulting in the formation of chemical bonds, challenging both traditional and modern core–valence distinctions. In addition, we argue that Cs 5p–5p bonding in CsCl occurs already at ambient pressure, stabilizing the B2 phase, and suggest experiments that may be able to detect signatures of such bonding.
