Deformation and stress at pop-in of lithium niobate induced by nanoindentation

The hardness of X-, Y- and Z-cut lithium niobate (LiNbO3 or LN) is 12.8, 9.1 and 10.6 GPa, respectively. The pop-in phenomenon was observed for all loading experimental data of nanoindentation, which was induced by the formation of twins, confirmed using sub-nanometer scale transmission electron microscopy. The maximum shear stresses at pop-in for X-, Y- and Z-cut LN wafers are 20.6, 13.3 and 18.4 GPa, respectively, and the corresponding stresses are 25.5, 21 and 20 GPa.