Second Harmonic Generation Investigation of Symmetry Breaking and Flexoelectricity Induced by Nanoindentations in SrTiO 3
Résumé
Strain gradients induced by nanoindentations in bulk undoped strontium titanate (SrTiO3) are investigated. After indenting a 850 nm deep pattern on the SrTiO3 surface with a 8 GPa hardness and an 83 GPa indentation modulus by a Berkovich tip, the resulting deformation patterns are imaged by Raman spectroscopy and by second harmonic generation microscopy. Cross‐shaped compressively stressed regions along the cubic SrTiO3 primary slip planes are observed. These zones relax toward the unstrained bulk material through localized strain gradients on a length scale of several microns. Second harmonic tomography reveals the reduction of the crystal's centrosymmetry in the vicinity of the crosslike features due to a strain gradient. These results indicate the appearance of flexoelectricity following the nanoindentation process due to the creation of an inhomogeneous strain.