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Ion Highway

The solid oxide fuel cell (SOFC) is an electrochemical device that converts chemical to electrical energy. It is usually based around an oxide conducting ceramic electrolyte that requires temperatures above 800°C to operate. One of the key limitations is in the transport of ions across the electrolyte. The most common electrolyte material used is Yttria-Stabilized Zirconia (YSZ). The ionic conductivity can be greatly affected by grain boundaries, dislocations, and point defects.

In ion highway study, dislocations were introduced by heavy ion irradiation. Irradiation with Xe+ or Ar+ produced a large number of point defects and dislocations via a mechanism similar to Frank partial dislocation formation. The dislocation density was on the order of 10¹²/cm² and the Burgers vector was 1/2<110>, as confirmed by cross-sectional high-resolution TEM and X-ray diffraction. Heat treatment at temperatures from 800-1400°C changed the defect structure, eliminated point defects, and allowed dislocations to react and grow.

Conductivity was measured using Electrochemical Impedance Spectroscopy (EIS) and Isotope Depth Profiling Technique (IEDP). To gain insight into the diffusion mechanism of vacancies in YSZ, quantum simulations using Density Functional Theory complemented with KMC technique was employed. Subsequently, the diffusion coefficients and the activation energies of the simulated diffusion process were extracted as a function of dislocation density and doping concentration.

Figure 1: High resolution TEM image showing a dislocation and the Burgers vector b
Figure 2: Schematic drawing of a dislocation