In-Situ Electrochemical Impedance Spectroscopy for Characterizing Transport Response during Material Irradiation
Authors: DeForest Tinsley Elizabeth , Derby Benjamin , Kennedy Ellis Rae , Schmidt Franziska , Valdez James , Wang Yongqian , Bhansali Shekhar , Uberuaga Blas , Kreller Cortney R. 
Published: December 2024

Radiation-induced crystalline disorder in complex oxides has a significant effect on the mass transport properties, namely the conductivity of the material. In the case of Gd2Ti2O7 (GTO) we observed that with increasing disorder, the conductivity of GTO subsequently increases. However, in the case of materials such as Yttria Stabilized Zirconia (YSZ), we observe a high radiation-tolerance to disorder and amorphization. Furthermore, the conductivity measured post-irradiation is comparable to the pristine state conductivity of YSZ. In theory, we might not see the permanent change in conductivity due to the inherent self-annealing propensity of YSZ. Such high rates of defect recombination may be masking any transport changes in the materials only present during the irradiation process. Thus, to elucidate these mass transport properties only present during irradiation we are developing an in-situ electrochemical impedance spectroscopy (EIS) method capable of experimentally probing the materials while they are undergoing irradiation.
With this novel in-situ EIS method we can extract information that would otherwise be missed in the standard ex-situ EIS characterization methods. Information such as: 1) rate of increase of conductivity between the onset of irradiation until steady state is reached, 2) the magnitude of such conductivity changes under irradiation at steady state, 3) the rate of decrease of conductivity once the beam is turned off until conductivity reaches a post-irradiation steady state. Although this is especially significant for materials that are radiation resistant, extracting the rate of increase of conductivity is also relevant and interesting for materials that are not as radiation resistant such as with GTO.
EIS is the preferred method for monitoring the electrical properties over other techniques such as with DC signals, because with the sinusoidal signals applied in EIS we extract these time-scale properties which make it possible to separate transport resistances from other rate-limiting processes. For the development of in-situ EIS: conductivity pathways, electrode geometries, beam path to the material, operating parameters of the potentiostat, and other considerations were made. Preliminary results for YSZ show that in the relatively lower operating temperature of 300 °C (far below the optimal temperature for high conductivity) the conductivity significantly increases when the irradiation beam is turned on, and quickly reverts to initial conductivity levels when the beam is turned off. Major contributions to the conductivity changes are attributed to the point defects created during the irradiation process. Thermal contributions of the beamline are excluded as the major contributor when comparing the temperature expected to reach the magnitude of conductivity change as well as the rate of decrease when the initial state of YSZ conductivity is recovered.

Figure 1. A) Electrode design used in preliminary experiments. B) Embedded electrode design for controlled area for more accurate conductivity calculations. C) Array of electrode geometries to optimize fabrication of embedded electrodes. D) Generalized example of ex-situ conductivity data. E) Generalized example of in-situ conductivity data.

Figure 1