Sb‐Triggered β‐to‐α Transition: Solvothermal Synthesis of Metastable α‐Cu 2 Se

Control over phase stabilities during synthesis processes is of great importance for both fundamental studies and practical applications. We describe herein a facile strategy for the synthesis of Cu 2 Se with phase selectivity through a simple solvothermal method. In the presence and absence of SbCl 3 , monoclinic α‐Cu 2 Se and cubic β‐Cu 2 Se can be synthesized, respectively. The formation of α‐Cu 2 Se requires optimization of the Cu/Se molar ratio in the starting reagents, the reaction temperature, as well as the timing for the addition of SbCl 3 . Differential scanning calorimetry of the synthesized α‐Cu 2 Se has shown that a part of it undergoes a phase transition to β‐Cu 2 Se at 135 °C, and that this phase transition is irreversible on cooling to ambient temperature. Kinetic studies have revealed that in the presence of Sb species the kinetically favored β‐Cu 2 Se transforms to the thermodynamically favored α‐Cu 2 Se. In this β‐to‐α phase transition process, the distribution of Cu ions in β‐Cu 2 Se, as determined by the Cu/Se ratio and temperature, is likely to play a crucial role.