Low energy bombardment induced cesium ion transport through a sodium ion conductor: Concentration profiles and diffusion coefficients

The bombardment of a sodium ion conductor with a low energy cesium ion beam is shown to induce ion transport in the sample, which involves the sodium as well as the cesium ions. This transport ultimately generates a macroscopic zone, where up to 95% of the sodium has been replaced by cesium. The zone where sodium and cesium coexist has been analyzed by means of the time-of-flight secondary-ion-mass-spectrometry. The experimental electro-diffusion profiles of the sodium and the cesium are quantitatively modeled by the Nernst–Planck–Poisson equations. The diffusion coefficient of the sodium is demonstrated to markedly depend on the local environment. It decreases by several orders of magnitude upon incorporation of the cesium ions.