Potassium self-diffusion in a K-rich single-crystal alkali feldspar

Abstract

The paper reports potassium diffusion measurements performed on gem quality single-crystal alkali feldspar in the temperature range from 1169 to 1021 K. Natural sanidine from Volkesfeld, Germany was implanted with 43 K at the ISOLDE/CERN radioactive ion-beam facility normal to the (001) crystallographic plane. Diffusion coefficients are well described by the Arrhenius equation with an activation energy of 2.4 eV and a pre-exponential factor of 5 × 10 −6 m 2 /s, which is more than three orders-of-magnitude lower than the 22 Na diffusivity in the same feldspar and the same crystallographic direction. State-of-the-art considerations including ionic conductivity data on the same crystal and Monte Carlo simulations of diffusion in random binary alloy structures point to a correlated motion of K and Na through the interstitialcy mechanism.

Multicomponent diffusion in ionic crystals: theoretical model and application to combined tracer- and interdiffusion in alkali feldspar

“…In Fig. 4 the diffusivities obtained from our experiments are compared with the calibrations for D * Na by Wilangowski et al (2015) and for D * K by Hergemöller et al (2017). Despite the fact that the experimental approach used by Wilangowski et al (2015) and by Hergemöller et al (2017) (tracer diffusion experiments) and our study are fundamentally different, the calibrations agree quite well.…”

“…The Na and K tracer diffusivities ⟂ (001) in Volkesfeld sanidine were determined experimentally by Wilangowski et al (2015) and by Hergemöller et al (2017). Using their Table 3 Diffusion coefficient for the smallest feasible…”

“…The calibration of D * K by Hergemöller et al (2017) is, however, rather uncertain, implying a considerable uncertainty also for the diffusivity ratio. The experimental data of Wilangowski et al (2015) and Hergemöller et al (2017) thus provide only weak additional constraints for the diffusivity ratio. In the absence of independent constraints on D * Na ∕D * K the diffusivities can only be determined to within the range given by the lower and upper bounds of the feasible parameter range.…”

Tracer diffusion in single crystalline CoCrFeNi and CoCrFeMnNi high entropy alloys

“…The diffusion experiments with implanted 64 Cu tracer atoms were performed at 3 different temperatures in a range of 973 − 1173 K. Figure 4 measuring, e.g., potassium self-diffusion in single crystalline alkali feldspar [37], and it is explained by the tracer evaporation at the external surface under vacuum conditions. Including the influence of distinctly increasing tracer concentration at the beginning of the penetration profiles, the volume diffusion coefficients, D V , can be determined using Strohm's solution [38] (solid lines in Fig.…”

The solid state physics programme at ISOLDE: recent developments and perspectives

“…This will greatly expand the possibilities of the diffusion programme at ISOLDE. Initial experiments with feldspar materials have been extremely promising where the properties of K diffusion have been measured [49]. In the coming years, a programme to understand the role of transition metals in technologically important materials such as CuInGaSe solar cells-one of the most efficient solar cell materials-will be followed where the unique possibilities offered at ISOLDE will be employed to understand the role of Cu diffusion in these materials, for which no current data yet exist.…”