Ionically Conducting Two-Dimensional Heterostructures

In the context of revealing interfacial effects on ion conduction, thin films are extremely worthwhile due to defined geometry. Of particular interest are heterostructures as they offer symmetric boundary conditions and a high density of hetero‐interfaces. The recent progress in this field is reviewed. Materials classes under concern include halides and oxides, and refer to various degrees of disorder and different mobilities. Even though in its infancy, the field of ionic heterostructures is already characterized by a variety of results of fundamental importance and of technological relevance. Ionically conducting two‐dimensional heterostructures advantageously allow investigation of interfacial effects on ionic conductivity, storage and reactivity. As the interface spacing continuously decreases from micrometer‐ down to nanometer‐scale, not only observation of size effects but also generation of a new artificial crystalline material can be achieved.