Atomic engineering of metastable BeO₆ octahedra in a rocksalt framework

An atomic structure is widely recognized as the key that determines the physical properties of a material. A critical challenge to engineer the atomic structure is that many useful crystals are metastable under ambient conditions and difficult to realize. Here, it is demonstrated that highly metastable atomic arrangements can be synthesized in the isostructural matrix via atomic layer deposition. Studying highly metastable BeO₆ octahedra in rocksalt MgO as a model system, it is experimentally and theoretically shown that the single-phase Be_xMg_1-xO thin films adopt rocksalt structure over wurtzite for the composition range x < 0.21. The single-phase rocksalt films exhibit almost doubled dielectric constants with the presence of BeO₆ octahedra. Such atomic environment engineering may create intriguing properties that have not been realized in the constituent materials. This work provides excellent opportunities to explore unprecedented materials properties via engineering metastable atomic arrangements using the isostructural matrix approach.