Structural analysis of a potassium hollandite K 1.35Ti 8O 16

Abstract

Crystals of K 1.35Ti 8O 16 have been investigated by single-crystal X-ray analysis, X-ray powder patterns, electron diffraction, and high-resolution electron microscopy. K 1.35Ti 8O 16 is obtained in the form of dark blue tetragonal crystals of the space group I4 m having the hollandite structure with a = 1018.8(2) pm and c = 296.61(7) pm. The refinement converges to a reliability factor of 0.025. The occupation of the T(2,2) tunnel sites in potassium is not statistical. Incommensurate one-dimensional superstructures were found by powder diffraction patterns as well as by electron diffraction. The multiplicity calculated from powder X-ray diffraction is m = 5.79 and that found by electron diffraction is m = 8.1; this is explained in terms of beam damage and loss of potassium within the T(2,2) sites. The final step in the decomposition is the formation of rutile from K 1.35Ti 8O 16 when all the potassium atoms are lost in the tunnels.