Experiment shows for the first time in detail how electrolytes become metallic

An international team has developed a sophisticated experimental technique at BESSY II to observe the formation of a metallic conduction band in electrolytes.

To accomplish this, the team first prepared cryogenic solutions of liquid ammonia containing different concentrations of alkali metals. The colour of the solutions changes with concentration from blue to golden as the individual atoms of metal in solution transition to a metallic compound. The team then examined these liquid jets using soft X-rays at BESSY II and subsequently has been able to analyse this process in detail from the data they acquired combined with theoretical predictions. The work has been published in Science and appears even on the cover.

What distinguishes metals from other materials is generally well understood. In a metal, some of the atoms’ outer electrons move through the crystalline lattice in what is called a conduction band. This is how metals conduct electric current. In contrast to metals, the ions in electrolytes are disordered and electrical conductivity even decreases with increasing ion concentration. So how does metallic behaviour arise from the many individual metal atoms dissolved in the electrolyte? At what concentration and exactly how does a conduction band form, and how do the electron orbitals behave during this process?

>Read more on the Bessy II (at HZB) website

Image: The theorists in the team have elaborately simulated the structure of the solvated electron in liquid ammonia.

Credit : Charles Universität Prag/O. Maršálek & T. Martinek