# Electron core ionization in compressed alkali metal cesium

## TL;DR

This paper investigates how high pressure causes electron core ionization in cesium, leading to changes in its electronic structure and complex crystal formations, with implications for understanding alkali metal behavior under extreme conditions.

## Contribution

It introduces a model explaining the formation of complex structures in compressed alkali metals through core electron ionization and band structure changes.

## Key findings

- Core ionization occurs at high compression levels.
- Valence electron count increases due to core overlap.
- Complex crystal structures emerge under high pressure.

## Abstract

Elements of group I in the Periodic table have valence electrons of s-type and are usually considered as simple metals. Crystal structures of these elements at ambient pressure are close-packed and high-symmetry of bcc and fcc types, defined by electrostatic (Madelung) energy. Diverse structures were found under high pressure with decrease of the coordination number, packing fraction and symmetry. Formation of complex structures can be understood within the model of Fermi sphere - Brillouin zone interactions and supported by Hume-Rothery arguments. With the volume decrease there is a gain in the band structure energy accompanied by a formation of many-faced Brillouin zone polyhedrons. Under compression to less than a half of the initial volume the interatomic distances become close to or smaller than the ionic radius which should lead to the electron core ionization. At strong compression it is necessary to assume that for alkali metals the valence electron band overlaps with the upper core electrons which increases the valence electron count under compression.

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Source: https://tomesphere.com/paper/1703.03972