Dislocation-based crack initiation and propagation in single-crystal SrTiO3

Understanding the irreversible deformation (dislocation activation and crack formation) of functional oxides, based on which various advanced electronic devices are fabricated, is critical for the optimal structural design and mechanical reliability. Here, we demonstrate the dislocation-based crack initiation and propagation in a model perovskite, single-crystal SrTiO3, at small scale. Using nanoindentation tests with spherical tips and etch pit study, we identify the sequence of the irreversible deformation events occurred in single-crystal (001) SrTiO3. For a locally stressed volume that is free of pre-existing cracks, the material undergoes the following processes: (1) purely elastic deformation; (2) dislocation activation on primary slip planes that are 45° inclined to the surface; (3) dislocation activation on secondary slip planes perpendicular to the surface; (4) crack initiation by dislocation pile-up; followed by (5) concurrent crack propagation and dislocation multiplication and motion at higher loads. Specifically, we focus on the crack formation caused by the dislocation pile-up beneath the spherical indenter. We also identify the favorable crack propagation planes to be {110} when the (001) surface is indented. These findings in cubic SrTiO3 are believed to be applicable for other ceramic materials with cubic structure.