NMR study of Ba2+ ion motion in one-dimensional ionic conductor with hollandite-type structure

Ionic motion of a divalent cation, Ba2+, in a single crystal of Ba-Al-priderite was studied using 27Al as an NMR probe. Several pairs of satellite peaks due to electric quadrupole interaction were observed superposed on broad satellite tails on both sides of the main peak of 27Al. These peak pairs indicate the existence of some stable three-dimensional configurations of Ba2+ ions in the structure, and the broad shoulders show a random substitution of Al3+ for Ti4+ sites. The temperature dependence of the spin-lattice relaxation time T*l measured in the temperature range from 161 to 1176 K was analyzed by a curve fitting method on the assumption that there are two types of Ba2+ ions. An activation energy of 0.47 eV was obtained for the motion of Ba2+ ions which are easy to move, and a broad distribution of activation energies spread over a range from 0.95 to 2.45 eV was obtained for the motion of Ba2+ ions which form a three-dimensional honeycomb framework and are hard to move. 17 refs.; 5 figs