Unraveling the Hall-Petch to inverse Hall-Petch transition in nanocrystalline CdTe

The transition from Hall-Petch to inverse Hall-Petch behaviors in nanocrystalline semiconductors is complex and remains poorly understood, despite its importance to the mechanical performance of these materials. In this study, we used molecular dynamics simulations with a machine-learning force field (ML-FF MD) to examine the shear deformation and failure mechanisms of nanocrystalline cadmium telluride (n-CdTe) across grain sizes ranging from 4.62 nm to 18.47 nm. Our results reveal a transition from Hall-Petch to inverse Hall-Petch behavior in n-CdTe at a critical grain size of -9.79 nm, where the material's maximum shear strength reaches about 1.23 GPa. This transition is driven by varying probabilities of phase transitions from the zinc-blende to the beta-Sn-like CdTe phase, due to the competition between shear localization and the availability of nucleation sites. Importantly, regardless of grain sizes, this phase transition often starts near grain boundaries (GBs), causing volume shrinkage and tensile stresses at GBs, further leading to fractures between grains. These findings offer valuable insights into the underlying mechanisms driving the transition from Hall-Petch to inverse Hall-Petch behavior as grain size decreases, as well as the failure behaviors observed in n-CdTe and other semiconductor materials.