The structure peculiarities of K 0.9 Fe 0.9 Ti 0.1 O 2 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.

A detailed analysis of correlations between structural features and cation conductivity is performed for KAlO(2) polymorphs in a wide temperature range of 300-1023 K. To explore the migration maps of K(+) cations we have used neutron diffraction data for low- and high-temperature KAlO(2) polymorphs and applied for the first time a novel algorithm based on the natural tiling concept and implemented it into the program package TOPOS. Five independent elementary channels for the K(+) cation migration have been revealed whose cross-sections were found to be essentially different in the low-temperature form, indicating a high anisotropy of the cation conductivity. During the transition to the cubic high-temperature phase all five channels become equivalent with sharply increased cross-sections that account for the jump-like increase of the cation conductivity and gives rise to its three-dimensional character.

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