  Soft clay-like Li-superionic conductors have been recently synthesized by
mixing rigid-salts. Through computational and experimental analysis, we clarify
how a soft clay-like material can be created from a mixture of rigid-salts.
Using molecular dynamics simulations with a deep learning-based interatomic
potential energy model, we uncover the microscopic features responsible for
soft clay-formation from ionic solid mixtures. We find that salt mixtures
capable of forming molecular solid units on anion exchange, along with the slow
kinetics of such reactions, are key to soft-clay formation. Molecular solid
units serve as sites for shear transformation zones, and their inherent
softness enables plasticity at low stress. Extended X-ray absorption fine
structure spectroscopy confirms the formation of molecular solid units. A
general strategy for creating soft clay-like materials from ionic solid
mixtures is formulated.
