Julia Zakel

Bombardment Induced Potassium Ion Transport Through a Sodium Ion Conductor: Conductivities and Diffusion Profiles

Abstract Ion transport through a Ca30 glass, a sodium ion (Na+) conductor, has been induced by bombardment with a potassium ion (K+) beam. The measurement of back side ion currents as a function of the ion beam kinetic energy by means of the recently developed BIIT (bombardment induced ion transport) approach allows determining the conductivity of the material. Measurement of this conductivity as a function of the temperature allows deriving the activation energy for ion transport as 0.99 eV ± 0.01 eV in perfect agreement with impedance spectroscopy. While the conductivity as well as the activation energy clearly correspond to the bulk property, i.e. the transport of Na+, depth profiling of the glass sample after the BIIT experiment exhibits K+ profiles reaching up to 100 nm into the glass. Ultimately, modeling of the experimental data by means of the Nernst–Planck–Poisson theory provides access to a quantitative understanding of the conductivities and the diffusion profiles under the condition of competing Na+/K+ ion transport.

Bombardment Induced Transport of Rb+ through a K+ Conducting Glass vs. K+ Transport through a Rb+ Conducting Glass

Abstract The transport of rubidium ions and potassium ions respectively through rubidium and potassium ion conducting glasses has been investigated by means of the recently developed low energy bombardment induced ion transport (BIIT) approach. Here, the combination of a bombarder ion M1 (Rb+,K+) and a charge carrier ion M2 (Rb+,K+), in short M1@M2, defines a 2 × 2 matrix where the diagonal elements refer to the native ion transport, Rb+@Rb+ and K+@K+, while the off-diagonal elements refer to foreign ion transport, Rb+@K+ and K+@Rb+. The latter corresponds to the transport of rubidium ions through a potassium ion conductor and vice versa. The native ion BIIT yields the intrinsic ionic conductivities and activation energies for ion hopping in line with impedance spectroscopic data also presented. The foreign ion BIIT leads to the generation of diffusion profiles up to 100 nm into the glass sample as revealed by time-of-flight secondary ion mass spectrometry (ToF-SIMS). The analysis of such depth profiles by means of Nernst–Planck-Poisson theory provides access to the concentration dependence of the diffusion coefficients. The concentration dependence of the potassium ion diffusion coefficient, D(K+), is markedly different for the rubidium glass vs. the potassium glass matrix. Within the error bars the concentration dependence of the rubidium ion diffusion coefficient, D(Rb+), is negligible in both glasses.

Potassium ion transport through poly-para-xylylene films

Bombardment of poly-para-xylylene films by a beam of potassium ions induces ion transport through the polymer material, which originally is an electrical insulator. The ion transport can easily be detected as neutralization current on an electrode at the back side of the film. The transport is accompanied by the formation of an electrodiffusion profile of potassium in the film as shown by time-of-flight secondary ion mass spectrometry. The potassium depth profiles can be rationalized by theoretical calculations based on numerical solving the Nernst-Planck-Poisson equations. The results may shed new light on the formation and dynamics of space charge zones in polymers and is thus potentially relevant for electret research.

Ionic conductivities of calcium-phosphate glasses

The transport of potassium and rubidium ions through glasses containing the respective alkali ion as mobile species has been investigated by means of bombardment induced ion transport (BIIT) and impedance spectroscopy (IS). The conductivities as well as the activation energies derived from the two approaches are in agreement lending further support to the recently developed BIIT approach.