Solid-phase flexibility in Ag₂Se semiconductor nanocrystals

Nanocrystals are known to alter the relative stability of bulk solid phases. Here we test the limits of this effect on Ag₂Se nanocrystals, a promising new electronic and infrared material. In the bulk, Ag₂Se exhibits a solid-solid phase transition to a superionic conducting phase at moderate temperatures. We map this phase transition as a function of size, temperature, and surface treatment in Ag₂Se core-only and core-shell nanocrystals. We show that the transition can be tuned not just below but also above the bulk phase-transition temperature. This phase flexibility has implications for applications in optoelectronic and phase-memory devices.