Metastable Tetragonal Cu2Se Hyperbranched Structures: Large-Scale Preparation and Tunable Electrical and Optical Response Regulated by Phase Conversion.

Despite the promising applications of copper selenide nanoparticles, an in-depth elucidation of the inherent properties of tetragonal Cu₂Se (β-Cu₂Se) has not been performed because of the lack of a facile synthesis on the nanoscale and an energy-intensive strategy is usually employed. In this work, a facile wet-chemical strategy, employing HCOOH as reducing agent, has been developed to access single-crystalline metastable β-Cu₂Se hyperbranched architectures for the first time. The process avoids hazardous chemistry and high temperatures, and thus opens up a facile approach to the large-scale low-cost preparation of metastable β-Cu₂Se hyperbranched architectures. A possible growth mechanism to explain the formation of the β-Cu₂Se dendritic morphology has been proposed based on time-dependent shape evolution. Further investigations revealed that the metastable β-Cu₂Se can convert into the thermodynamically more stable cubic α-Cu_{2− x}Se maintaining the dendritic morphology. An increase in electrical conductivity and a tunable optical response were observed under ambient conditions. This behavior can be explained by the oxidation of the surface of the β-Cu₂Se hyperbranched structures, ultimately leading to solid-state phase conversion from β-Cu₂Se into superionic conductor α-Cu_1.8Se, which has potential applications in energy-related devices and sensors. [ABSTRACT FROM AUTHOR]