Exploring the Possibility of Extrinsic Anion Vacancies in Li6PS5Cl

The search for superionic conductors requires a deep understanding of the underlying crystal structure and local dynamic processes. Therefore, cationic and anionic substitutions are typically performed to monitor the resulting changes in the structure and ionic transport, ultimately drawing conclusions to find optimized Li+ conductors. Within a substitution series, the anionic framework is generally assumed to be fully occupied in contrast to defective cationic substructures. This study addresses the question of whether the targeted introduction of extrinsic anion vacancies can be stabilized within a Li+ argyrodite with the help of a targeted Li6(PS4)S1+x/2□x/2Cl1−x substitution series. Furthermore, by not changing the amount of Li+ in the structure, there could be a possibility to decouple Li+ carrier density effects from anion influence on Li+ transport. Using diffraction and spectroscopic techniques, Monte Carlo simulations, as well as density functional theory calculations, changes in crystal structure and ionic and electronic transport are monitored, and the configurational stability is assessed. The structures with anion vacancies were found to have high formation energies, in agreement with the experimental observation. Instead, the phase formation of Li6+xPS5+xCl1−x is observed, showing a decrease in Li+ conductivity related to the anion ordering.