Spherical nanoindentation study of the deformation micromechanisms of LiTaO3 single crystals

Herein, spherical nanoindentation (NI) was used to investigate the room temperature deformation behavior of C-plane LiTaO3 single crystals loaded along the [0001] direction as a function of ion irradiation. When the NI load-displacement curves of 3 different nanoindenter radii (1.4 mu m, 5 mu m, and 21 mu m) were converted to NI stress-strain curves, good agreement between them was found. The surface first deforms elastically - with a Young's modulus of 205 +/- 5 GPa, calculated from the stiffness versus contact radii curves and 207 +/- 3 GPa measured using a Berkovich tip - and then plastically deforms at approximate to 6 GPa. Repeated loading into the same location results in large, reproducible, fully reversible, nested hysteresis loops attributed to the formation of incipient kink bands (IKBs). The latter are coaxial fully reversible dislocation loops that spontaneously shrink when the load is removed. The IKBs most probably nucleate within the (10 (1) over bar2) twins that form near the surface. The sharper radii resulted in twin nucleation at lower stresses. The changes in the reversible loops' shape and areas can be related to the width of the twins that form. The latter were proportional to the nanoindenter tip radii and confirmed by scanning electron microscopy and by the fact that larger threshold stresses were needed for IKB nucleation with the smaller tip sizes. No effect of irradiation was observed on the NI response, presumably because of the mildness of the irradiation damage. (C) 2011 American Institute of Physics. [doi:10.1063/1.3608158]