Ba with Unusual Oxidation States in Ba Chalcogenides under Pressure
Fei Li, Xiaohua Zhang, Yang Fu, Yanchao Wang, Aitor Bergara, Guochun Yang
Abstract
The preparation of compounds with novel atomic oxidation states and emergent properties is of fundamental interest in chemistry. As s-block elements, alkali-earth metals invariably show a +2 formal oxidation state at normal conditions, and among them, barium (Ba) presents the strongest chemical reactivity. Herein, we propose that novel valence states of Ba can be achieved in pressure-induced chalcogenides, where it also shows a feature of 5d-elements. First-principles swarm-intelligence structural search calculations identify three novel stoichiometric compounds: BaCh4 (Ch = O, S) containing Ba2+, Ba3Ch2 (Ch = S, Se, Te) with Ba+ and Ba2+, and Ba2Ch (Ch = Se, Te) with Ba+ cations. The pressure-induced drop of the Ba 5d level relative to Ba 6s is responsible for this unusual oxidation state. These compounds display captivating structural characters, such as Ba-centered polyhedra and chain-shaped Ch units. More interestingly still, the interaction between two Ba+ ions ensures their structural stability.