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

X-ray diffraction measurement for a single crystal of NaxCrxTi8−xO16 (x≈1.7) has been performed at 773 K. The structure is characterized by a host framework containing one-dimensional tunnels extending along the c axis. The tunnel is described as an infinite chain of pseudocuboctahedral cavities where Na+ ions are located. The Na sites in a cavity deviate from the cavity center in directions normal to or along the tunnel axis. A bottleneck, i.e. a boundary of adjacent cavities, is also used as a Na position. These results are basically the same as those obtained at room temperature. An electron density map at section x=0 obtained from the maximum entropy 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 from the electron density distribution along the tunnel.