Real time observation of oxygen diffusion in CGO thin films using spatially resolved Isotope Exchange Raman Spectroscopy

TL;DR

This paper introduces a novel, cost-effective in situ isotope-exchange Raman spectroscopy method for real-time analysis of oxygen diffusion in CGO thin films, providing high temporal resolution and new insights into ionic transport mechanisms.

Contribution

The study presents a new experimental technique combining Raman spectroscopy with isotope exchange to measure oxygen diffusion in thin films with unprecedented time resolution.

Findings

Measured diffusion coefficients for CGO thin films at 300-500°C.

Validated the method through FEM simulations and literature comparison.

Demonstrated the technique's applicability for studying ionic transport in functional materials.

Abstract

The exploitation of advanced materials for novel energy, health and computing applications requires fundamental understanding of enabling physicochemical mechanisms, including ionic and electronic conductivity, defect formation processes and reaction kinetics. Therefore, access to underlying constants of functional materials via advanced but straightforward experimental techniques is key. We present a novel, cheap and widely applicable approach to analyze oxygen-tracer-diffusion in thin films with unprecedented time resolution based on the novel in situ isotope-exchange Raman spectroscopy (IERS) methodology. Raman spectroscopy is sensitive to changes in the local isotopic composition, manifested by a frequency shift of the oxygen Raman modes. Employing a Raman transparent capping layer allows to establish an in-plane tracer gradient and follow the isotope exchange and diffusion processes via consecutive spatial and time resolved in situ Raman line scans. Mass-transport coefficients are calculated from these isotopic gradients, similar to conventional techniques, but with an additional time-component, not accessible by other techniques. Here, we study gadolinium doped ceria (CGO) thin films, capped with Si3N4 or Al2O3. We report diffusion coefficients within the temperature range of interest for intermediate temperature emerging applications (300-500{\deg}C) and confirm the validity of the measurement procedure and extracted parameters by comparison with FEM simulations and literature results.