Thermal Stability of Metal Nanocrystals: An Investigation of the Surface and Bulk Reconstructions of Pd Concave Icosahedra

Despite the remarkable success in controlling, the synthesis of metal nanocrystals, it still remains a grand challenge to stabilize and preserve the shapes or internal structures of Metastable kinetic products. In this work, we address this issue by systematically investigating the surface and bulk reconstructions experienced by a Pd concave icosahedron when subjected to heating up to 600 degrees C in vacuum. We used in situ 'high resolution transmission electron microscopy to identify the equilibration, athways of this far-from-equilibrium structure. We were were able to capture key structural transformations occurring during the thermal annealing process, which were mechanistically rationalized, by implementing self-consistent plane-wave density functional theory (DFT) calculations. Specifically, the concave icosahedron was found to evolve into a regular itosaliedron via surface reconstruction in the range of 200-400 degrees C,, and then transformintd,,pseildospherical, crystalline Structure-through bulk 'reconstruction when further heated to. 600 degrees C. The mechanistic understanding May lead-to, the development of strategies for enhancing the thermal stability of metal nanocrystals.