Incipient plasticity in SrTiO₃ influenced by Nb-doping and displacement rate

Understanding the onset of plasticity in SrTiO₃ (STO) is critical for enhancing its mechanical performance and reliability in functional applications. Despite known influences of doping and loading conditions, their combined effects on dislocation nucleation in STO remain underexplored. In this study, we investigate the incipient plasticity of (001)-oriented STO single crystals by systematically varying displacement rates and incorporating Nb doping, using displacement-controlled nanoindentation and first-principles calculations. We reveal a non-monotonic dependence of the critical shear stress on displacement rate, governed by the interplay between stress relaxation and thermal activation time. Nb doping is shown to reduce the critical stress for dislocation nucleation by lowering the stacking fault energy along the <100> direction and altering the local charge environment, as evidenced by density functional theory (DFT) and Bader charge analysis. These insights advance the understanding of deformation mechanisms in functional ceramics and offer practical guidance for tailoring their mechanical responses through defect and doping engineering.