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CO 2 adsorption on a barium oxide (BaO) surface saturated with a monolayer of H 2 O molecules was studied; a monolayer of H 2 O molecules on the BaO surface exhibits nondissociative or dissociative adsorption. During the nondissociative reaction, a hydroxyl ion-terminated surface is produced, resulting in the formation of barium hydroxide (Ba(OH) 2 ) on the surface. The Ba(OH) 2 from the substrate associates with the tightly bound CO 2 molecule, resulting in the formation of barium carbonate (BaCO 3 ). In contrast, during the dissociative H 2 O adsorption, a hydrogen-terminated surface is produced, which strongly adsorbs CO 2 molecules. The H 2 O molecules on a fully saturated BaO surface (containing multiple layers of H 2 O molecules) readily aggregate, and Ba dissociation takes place on the hydrated surface, possibly resulting in a surface containing Ba defects.

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The magnetic structure and the origin of band gap opening for Ba2CuOsO6 were investigated by exploring the spin exchange interactions and employing the spin–orbit coupling effect. It revealed that the double-perovskite Ba2CuOsO6, composed of the 3d (Cu2+) and 5d (Os6+) transition metal magnetic ions is magnetic insulator. The magnetic susceptibilities of Ba2CuOsO6 obey the Curie–Weiss law, with an estimated Weiss temperature of −13.3 K, indicating AFM ordering. From the density functional theory approach, it is demonstrated that the spin exchange interaction between Cu ions plays a major role in exhibiting an antiferromagnetic behavior in the Ba2CuOsO6 system. An important factor to understand regarding the insulating behavior on Ba2CuOsO6 is the structural distortion shape of OsO6 octahedron, which should be closely connected with the ionic size of the A-site ion. Since the d-block of Os6+ (d2) ions of Ba2CuOsO6 is split into four states (xy < xz, yz < x2–y2 < z2), the crucial key is separation of doubly degenerated xz and yz levels to describe the magnetic insulating states of Ba2CuOsO6. By orbital symmetry breaking, caused by the spin–orbit coupling, the t2g level of Os6+ (d2) ions is separated into three sublevels. Two electrons of Os6+ (d2) ions occupy two levels of the three spin–orbit-coupled levels. Since Ba2CuOsO6 is a strongly correlated system, and the Os atom belongs to the heavy element group, one speculates that it is necessary to take into account both electron correlation and the spin–orbit coupling effect in describing the magnetic insulating states of Ba2CuOsO6.