 Abstract Metavalent Bonding, MVB, is a unique phenomenon observed in certain crystal structures, which involves the competition between electron delocalization and electron localization. This phenomenon is particularly important in phase change materials used in advanced memory applications. In this study, the authors investigated the effect of MVB on the structural and optical properties of two different materials, SB2TE3 and Gouis-Bite alloys. They found that MVB can be manipulated by applying uniaxial strain, resulting in a large variation of dielectric function and reflectivity in the trigonal phase. Finally, they proposed strategies for applications utilizing the trigonal phase. This article was authored by Wei Zhang, Heng Ming Zhang, Su Yang Sun, and others.