High-temperature X-ray study for a single crystal of the hollandite-like one-dimensional ionic conductor, NaxCrxTi8-xO16 (x approximate to 1.7)

X-ray diffraction measurement for a single crystal of NaxCrxTi8-xO16 (x app roximate to 1.7) has been performed at 773 K. The structure is characterize d by a host framework containing one-dimensional tunnels extending along th e c axis, The tunnel is described as an infinite chain of pseudocuboetahedr al cavities where Na+ ions are located. The Na sites in a cavity deviate fr om the cavity center in directions normal to or along the tunnel axis. A bo ttleneck, i.e. a boundary of adjacent cavities, is also used as a Na positi on. These results are basically the same as those obtained at room temperat ure. An electron density map at section x = 0 obtained from the maximum ent ropy method was naturally more broad at 773 K than at room temperature. The Na+ ion suffers almost no bottlenecking effect, even at 773 K, judging fro m the electron density distribution along the tunnel. (C) 2000 Elsevier Sci ence B.V. All lights reserved.