Ionic Conductivity in Ti-Doped KFeO2: Experiment and Mathematical Modeling

The structure peculiarities of K0.9Fe0.9Ti0.1O2 that favor the emergence of a superionic state have been studied using neutron powder diffraction data as a function of temperature. The migration paths in the structure of both undoped and doped potassium ferrite were modeled by topological (tiling) and DFT methods. It is shown that heating of the low-temperature phase leads to increase of the ionic conductivity thanks to widening the migration channels and the appearance of thermally induced cation vacancies. The calculated migration barrier is found to not exceed 0.3 eV/ion in all phases, which is consistent with the experimental data. Doping also increases the ionic conductivity, but up to about 10% of Ti only; then the experimental activation energy even increases. The DFT modeling shows that it can be caused by growth of the regions unavailable for the mobile cations; the regions are formed around the dopant atoms.