X-ray diffraction measurements of a single crystal of Ti6.3Na1.7Cr1.7O16 were performed at 773K. The structure was characterized by a host framework which contained 1-dimensional tunnels that extended along the c-axis. Such tunnels could be described as being infinite chains of pseudo-cuboctahedral cavities within which Na ions were located. The Na sites in a cavity deviated from the cavity center in directions which were normal to, or along, the tunnel axis. A bottleneck (boundary of adjacent cavities) was also used as a Na position. The results were essentially the same as those obtained at room temperature. The electron density map, as deduced by using the maximum entropy method, was broader at 773K than at room temperature. It was found that the Na+ ion suffered almost no bottleneck effect, even at 773K, as judged from the electron density distribution along the tunnel.

High-Temperature X-Ray Study of a Single Crystal of the Hollandite-Like One-Dimensional Ionic Conductor Ti6.3Na1.7Cr1.7O16. Y.Michiue, M.Watanabe, S.Yoshikado: Solid State Ionics, 2000, 136-137, 939-43