Nanoscale Stabilization of Nonequilibrium Rock Salt BiAgSeS: Colloidal Synthesis and Temperature Driven Unusual Phase Transition

Abstract

Stabilization of nonequilibrium phases of inorganic solids is an art in synthetic chemistry. Herein, we demonstrate the entrapping of nonequilibrium rock salt phase of BiAgSeS in the nanocrystalline form at room temperature via kinetic colloidal synthesis. High symmetry rock salt nanocrystals undergo an unusual irreversible phase transition to a lower symmetry thermodynamic trigonal structure upon thermal treatment. To get fundamental insights into such unusual finding, we have performed temperature dependent synchrotron powder X-ray diffraction, positron annihilation spectroscopy, and density functional theory based structural energy and phonon modes investigations. Kinetically trapped strained rock salt BiAgSeS nanocrystals irreversibly transform to thermodynamically stable trigonal structure upon heating via Ag–Bi exchange, which is alleviated by a significant increase in the Ag vacancy.