The novel IERS method, based upon the Raman frequency shift due to the changes in isotope concentration, has been demonstrated as a powerful technique to study the oxygen diffusion and surface exchange kinetics in situ with unprecedented time resolution. However, the existence of at least one active oxygen vibrational Raman mode is the prerequisite to apply IERS to characterize oxygen transport of a given material. This confines its application to a limited range of materials, with its applicability determined on a case-by-case basis.
To address this limitation, we demonstrate that by an innovative method, it is possible to apply this novel universal IERS technique to study the oxygen surface exchange dynamics independent of the vibrational properties of the functional materials. A multilayer thin film configuration has been designed with the main components of the functional layer, the probe layer, and the blocking layer. It is anticipated that this universal IERS method will quickly establish itself as a standardised in situ methodology for studying ion transport dynamics, benefiting research on ionic conducting and mixed materials for a broad range of solid-state electrochemical energy devices.
In addition, the IERS technique has been extended to bulk samples. Our results provide significant insights for understanding the structure, defect chemistry, composition, and oxygen mass transport dynamics in the doped ceria single phase and dual phase composites, where the oxygen surface exchange and bulk diffusion kinetics are in good agreement with the secondary ion mass spectrometry (SIMS) results. This study will be a starting point for more sophisticated and quantitative analysis on broader solid state ionic materials systems, particularly combined with more advanced data analysis techniques involved with machine learning.
Furthermore the IERS was carried out to understand the environmental effects. A combination of different in situ kinetic measurements such as Raman, electrical conductivity relaxation and time-resolved X-ray diffraction was applied to achieve holistic information on structure, mass and charge transport.