Critical Size for Fracture during Solid−Solid Phase Transformations

The study of nanoscale materials with well-controlled size and shape can be used to learn more about critical length scales for numerous physical and chemical phenomena in solids and extended systems. 1,2 Small nanocrystals (below 5-nm diameter) have been shown to exhibit fully reversible single-domain structural phase transformations with large volume changes over multiple cycles. The same transformations in extended solids are accompanied by irreversible domain formation. 3-5 Here we investigate the crossover between these regimes by studying a pressure-induced structural transformation in 4-nm-diameter nanorods varying in aspect ratio from 1 to 10. We find that above a critical length the nanorods fracture at the moment of the structural transformation. This work demonstrates the use of simple, well-defined nanoscale systems to examine fundamental structural phenomena found in extended solids.