Li6+2x[B10Se18]Se-x (x approximate to 2), an ion-conducting double salt

Hammerschmidt A, Doch M, Putz S, Eckert H, Krebs B

Abstract

Li6+2x[B10Se18]Se-x (x approximate to 2) was prepared in a solid state reaction from lithium selenide, amorphous boron and selenium in evacuated carbon coated silica tubes at a temperature of 800 degrees C. Subsequent cooling from 600 degrees C to 300 degrees C gave amber colored crystals with the following lattice parameters: space group I2/a (at 173 K); a = 17.411 (1) angstrom, b = 21.900(1) angstrom, c = 17.820(l) angstrom, beta = 101.6(1)degrees. The crystal structure contains a well-defined polymeric selenoborate network of composition ([B10Se16Se4/2](6-))(n) consisting of a system of edge-sharing [B10Se16Se4/2] adamantanoid macro-tetrahedra forming large channels in which a strongly disorderd system of partial occupied Li+ cations and additional disordered Se2- anions is observed. The crystal structure of the novel selenoberate is isotypic to Li6+2x[B10S18]S-x (x approximate to 2) [1]. X-ray and Li-7 magic-angle spinning NMR data suggest that the site occupancies of the three crystallographically distinct lithium ions exhibit a significant temperature dependence. The lithium ion mobility has been characterized by detailed temperature dependent NMR lineshape and spin-lattice relaxation measurements.