Indentation size effect and dislocation structure evolution in (001) oriented SrTiO3 Berkovich indentations: HR-EBSD and etch-pit analysis

In the present work, the dislocation structure evolution and indentation size effect in (001) oriented STO have been studied by using sequential polishing, chemical etch-pit technique and high-resolution electron backscattered diffraction (HR-EBSD) analysis via Berkovich nanoindentation experiments. Nanoindentation load-displacement curves show multiple pop-in events, which relate to nucleation and extension of dislocation pile-ups around the residual impression. Sequential polishing and etching revealed the three-dimensional dislocation etch-pit structure at various sub-surface depths. The dislocation densities are determined for a 5 mN and 10 mN indentation below the surface via HR-EBSD and etch-pit analysis. With HR-EBSD, the lattice rotation and thereby GND densities are determined, while the etch-pit technique revealed the total dislocation density. Based on the independently measured dislocation densities, we clearly show a depth dependent dislocation density, where both total and GND densities increase with decreasing indentation depths. The higher dislocation densities below smaller indents explain the observed size dependency of the hardness in STO, which also sheds light on the extraordinary combination of high indentation hardness and low yield strength in STO.

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