Structure and Ionic Conductivity of Li-Disordered Bismuth o-Thiophosphate Li_60-3x Bi_16+x (PS₄)₃₆

The structure of the first lithium-containing bismuthortho (o)-thiophosphate was determined using a combinationof powderX-ray, neutron, and electron diffraction. Li60-3x Bi16+x (PS4)(36) with x in the range of 4.1-6.5possesses a complex monoclinic structure [space group C2/c (No. 15)] and a large unit cell with the latticeparameters a = 15.4866 & ANGS;, b = 10.3232 & ANGS;, c = 33.8046 & ANGS;, and & beta;= 85.395 & DEG; for Li44.4Bi21.2(PS4)(36), in agreement with the structure as observed by X-rayand neutron pair distribution function analysis. The disordered distributionof lithium ions within the interstices of the dense host structureand the Li ion dynamics and diffusion pathways have been investigatedby solid-state nuclear magnetic resonance (NMR) spectroscopy, pulsedfield gradient NMR diffusion measurements, and bond valence sum calculations.The total lithium ion conductivities range from 2.6 x 10(-7) to 2.8 x 10(-6) S cm(-1) at 20 & DEG;C with activation energies between0.29 and 0.32 eV, depending on the bismuth content. Despite the highlydisordered nature of lithium ions in Li60-3x Bi16+x (PS4)(36), the underlying dense host framework appears to limit the dimensionalityof the lithium diffusion pathways and emphasizes once more the necessityof a close inspection of the structure-property relationshipsin solid electrolytes. Different analyticaltechniques were used to characterizethe structure and to investigate the ionic transport properties. Thecombination of these techniques allowed us to elucidate the complexstructure of the first lithium-containing bismuth o-thiophosphate and provide insights into the electrochemical andionic diffusion properties.