Structural Analysis of a Potassium Hollandite K1.35Ti8016

Crystals of K1.35Ti8016 have been investigated using single-crystal X-ray analysis, X-ray powder patterns, electron diffraction, and high-resolution electron microscopy to understand their structural characteristics. The primary objective was to elucidate the structural properties of the potassium hollandite, specifically its crystal structure and the behavior of potassium within the T(2,2) tunnel sites. Findings revealed that K1.35Ti8016 forms dark blue tetragonal crystals belonging to the space group 14/m, with specific lattice parameters identified as a = 1018.8(2) pm and c = 261.7(7) pm. The refinement process achieved a reliability factor of 0.025, indicating strong confidence in the structural results. An important observation was that the occupation of the tunnel sites was non-statistical, with the formation of incommensurate one-dimensional superstructures detected via various diffraction techniques. The multiplicity measurements varied for powder X-ray and electron diffraction, attributed to beam damage and potassium loss. The ultimate decomposition process leads to rutile formation from K1.35Ti8016 following the loss of potassium ions from the tunnels, emphasizing the dynamic behavior of the hollandite structure under studied conditions.