The structure of a one-dimensional (1d) K ion conductor KxMgx/2Ti8-x/2O16 has been refined at 250 K and 150 K by a single-crystal X-ray diffraction technique. Probability density functions (PDFs) for the K ion were obtained from the structure model considering possible local structures in a hollandite 1d tunnel. The joint-PDFs were calculated for specific K sites concerning the hopping process in the tunnel. Temperature dependence of the joint-PDF was explained by a simple thermal activation, indicating no phase transition. (C) 2010 Elsevier B.V. All rights reserved.