Transport properties of solid electrolytes: Effect of the isotope composition of lithium charge carriers

The isotope composition of lithium charge carriers is experimentally found to severely affect transport in solid electrolytes alpha-Li3BO3, Li3N, Li3AlN2, Li5SiN3, Li6MoN4, Li6WN4, and LiCl. The lithium cation conduction of these decreases with increasing content of Li-6 or Li-7 and reaches a minimum at [Li-6] = [Li-7]. The activation energy for conduction increases, reaches a maximum in the same compositions, and then diminishes. Rates of spin-lattice relaxation of Li-7 nuclei in electrolytes are studied by an NMR method at 15-35 MHz. The calculated activation energy for short-range motion (to one interatom distance) of lithium charge carriers in crystal lattices of electrolytes is lower than that for ionic conduction by 2-3 times, which is attributed to two types of correlation (electrostatic, isotopic) of charge carriers.