Caesium (Cs) is an alkali metal that combines well with oxygen to form cesium oxide and other oxide compounds. The element is silvery gold in color and has vibrant blue lines in its spectrum, giving it the name “sky blue.” Caesium is very soft and ductile and is used in the production of ceramics, light weight structural components for aerospace and electrochemical applications where ionic conductivity is needed. The oxide compounds of the element are basic anhydrides and react rapidly with acids and strong reducing agents in redox reactions.

cesium oxide is a complex material, but has low work function and high carrier mobility, making it useful in photodetection. It is also used in the preparation of negative electron affinity devices, where it can reduce the work function on a variety of metal surfaces to significantly improve device performance and lifetime.

The structure of cesium oxide has been investigated using high resolution transmission electron microscopy (TEM) and has been found to have a closed-cage fullerene-like structure. The atomic arrangement in the crystalline structure of the compound has been confirmed by x-ray crystallography and the atomic orbits are very similar to those of the related compounds Cs18Tl8O6 and Cs18Hg8O6, with identical occupancies of sites with equal Wyckoff letters.

The calculation of the density of states shows several distinct features that confirm non-metallic behaviour of the compound, including a large band gap and three bands below the Fermi level corresponding to the p atomic orbitals in the [Hg8]6- cluster anion. The bands have narrow dispersion and are located in the energy range -1.9 to -1.1 eV.