The high-pressure behaviour of Cs is believed to result from pressure-driven s-to-d electron transfer, which results in a number of structural phase transitions and unusual optical and melting behaviour. In addition, the s-to-d transition changes the bonding character of Cs from the non-directional bonding of a nearly-free electron metal at ambient pressure to more complex directional bonding at high pressures. As a result, Cs transforms from simple structures to more complex open-packed structures on pressure increase. It is only recently that the structure of Cs-V has been reported, and that Cs-III, long supposed to be fcc, has been shown to have a complex orthorhombic structure with 84 atoms per unit cell. Calculations of the electron density in Cs-IV and in the predicted high-pressure complex phases of Li and Na, suggest that in each structure there should be interstitial electron density between the atomic sites. Indeed, it may be possible to regard Cs-IV as 'Cesium electride' Cs+e-.
This is a weekly series of informal talks given primarily by members of the soft condensed matter and statistical mechanics groups, but is also open to members of other groups and external visitors. The aim of the series is to promote discussion and learning of various topics at a level suitable to the broad background of the group. Everyone is welcome to attend..