Specific features of the crystal structure of polymorphous modifications of KFeO$_2$ and their correlation with ionic conductivity

The structure of potassium ferrite KFeO$_2$ has been studied by high-temperature powder neutron diffraction over a wide temperature range. Based on the structural data, the sizes of potassium cation migration channel have been found in the low- and high-temperature KFeO$_2$ modifications using the TOPOS program package. In the low-temperature form, the channels are nonequivalent, and, as a result, strong anisotropy of the potassium-cation conductivity is observed. During the phase transition, the migration channel sizes increase and are equalized, which is the main cause of the jump in the conductivity.