Compressibility Studies of Copper Selenides Obtained by Cation Exchange Reaction Revealing the New CsCl Phase

In this study, we performed a detailed high-pressure study on Cu2-xSe nanostructures created through cation exchange reactions from CdSe nanocrystals (NCs). These structures exhibited two shapes: zinc blende faceted NCs and wurtzite nanoplatelets (NPLs). Using the diamond anvil cell technique, we examined the phase transitions of Cu2-xSe NCs, particularly the B1 phase with Fm-3m symmetry, under pressures up to 40 GPa. We discovered unique structural changes in Cu2-xSe NCs, different from those in zinc blende CdSe NCs and bulk Cu2-xSe. A novel CsCl-type lattice (B2 phase) with Pm-3m symmetry was observed above 4 GPa, a phase not previously seen experimentally in copper selenides. This CsCl-type lattice showed partial retention after decompression. We also explored how the shape and uniformity of these nanostructures affect their structural stability. This insight into copper selenides' phase behavior is crucial for future applications, and the discovery of a new phase in copper selenide marks a significant advancement in the exploration of novel material phases with potentially unique properties.