The School of Mechanical and Materials Engineering Seminar Series, “Tailoring Plasticity in Brittle Materials through Doping and Light Modulation” Presented by Dr. Qi An

About the event

Tailoring Plasticity in Brittle Materials through Doping and Light Modulation

Presented by Dr. Qi An, Associate Professor, Department of Materials Science and Engineering, Iowa State University

Abstract
Controlling the plasticity of brittle materials remains a major challenge in materials science, especially for superhard ceramics and semiconductors, where strong directional bonding often leads to limited deformability and catastrophic failure. In this seminar, I will discuss how plasticity can be modified through two conceptually related approaches—chemical doping and light modulation—using a quantum-mechanics-based computational framework that integrates density functional theory (DFT), constrained DFT, and machine-learning force fields (ML-FFs). These methods enable us to probe how bonding and defect behavior govern deformation in covalent and partially covalent materials. In the first part, I will focus on superhard boron carbide (B₄C), whose intrinsic brittleness is closely linked to its complex icosahedral structure and strong covalent bonding. Our DFT and ML-FF simulations show that brittle failure in single-crystal B₄C originates from the formation of high-density amorphous shear bands caused by fracture of the icosahedra. Large-scale shock simulations of nanocrystalline B₄C further identify grain-boundary sliding, intergranular amorphization, and intragranular amorphization as the dominant deformation mechanisms. These insights suggest that doping can effectively modify plasticity. In particular, Al microalloying changes the dominant deformation mode from amorphization to dislocation nucleation and glide by weakening the C–B–C chain bonding. In the second part, I will discuss light-modulated plasticity in semiconductors. Our DFT and constrained-DFT-based ML-FF studies show that photoexcited electron-hole pairs can strongly alter local bonding, stacking-fault energetics, and dislocation behavior. In ZnS, photoexcitation changes deformation from a dislocation-mediated mode to twinning-dominated brittle failure. We further show that light increases the Peierls stress in ZnS by redistributing strain from the dislocation core to the matrix, thereby reducing dislocation mobility. Together, these results demonstrate that both doping and light modulation provide powerful routes to tailor plasticity in brittle materials.

Biography
Dr. Qi An is an Associate Professor in the Department of Materials Science and Engineering at the Iowa State University. He received his MS and PhD degrees in Materials Science from Caltech, and his BS degree from the University of Science and Technology of China. His research area is computational materials science covering machine learning, electronic structure calculations and atomistic simulations. His research specifically focuses on photomechanical behaviors of semiconductors, mechanical properties of ceramics and thermoelectric materials; computational alloy design; metallic glasses; material behaviors under extreme conditions; and heterogeneous catalysis. He has authored or co-authored over 220 publications in scientific journals.