Flash sintering of ionic conductors: The need of a reversible electrochemical reaction

Flash sintering (FS) is a current-assisted sintering technique able to densify ceramics in short periods of time (just a few seconds) at temperatures significantly lower than in conventional sintering processes. FS technique was firstly reported for yttrium-stabilized zirconia and later it had been proved successful for a large range of oxide materials that present ionic conduction by oxygen vacancies. This paper describes the use of FS on a sodium ion conductor based on a model compound, the beta-alumina. Different electrode materials have been tested, i.e., silver and platinum. The impact of the electrode reaction on the current flow, and thus, on the sintering efficiency is shown for the first time. It appears that the densification by FS can only be possible if the current collectors, i.e., the electrodes, are specifically designed to enable reversible electrochemical reactions at the interfaces between the electrodes and the ionic compound, insuring the current flow through the powder compact.