Self‐Straining Nanocrystals Strategy: Temperature and Pressure Co‐Induced Phase Transitions of CsPbBr3 in Amorphous Matrices

Abstract Understanding temperature and pressure co‐induced structural evolution of nanocrystals (NCs) is important for the design and application of heterostructure devices. However, the phase transition and band structure change are difficult to be analyzed under temperature and negative pressure co‐induced conditions. Here, an adjustable self‐straining strategy to control the temperature and pressure co‐induced phase transitions of NCs in amorphous matrices is reported. The synchronous pressure regulation, based on the thermal expansion mismatch between the NCs and the amorphous matrix, can be achieved by changing a single temperature variable. Two new phase transition processes of CsPbBr 3 NCs, including monoclinic‐orthorhombic and reversible amorphization, are clarified for the first time using the proposed self‐straining strategy. Besides, all the phase transition temperatures of the self‐straining NCs show a high sensitivity response to the pressure regulation. Most importantly, the encapsulation of CsPbBr 3 NCs in an amorphous matrix excludes the effect of external environments allowing the elucidation of the widely existing “self‐straining effect” in the NCs with heterogeneous structures. This work provides a better fundamental understanding of the phase transitions of NCs and paves the way toward the development of an in situ method to predict the multiphysics co‐induced structural evolution of NCs in optoelectronic devices.