Nanohardness and crack resistance of HTS YBCO thin films

Nanoindentation and nanoscratching using atomic force microscope (AFM) were employed to study the local mechanical properties of high TC superconductors YBCO thin films featuring high critical current density. Two YBCO films sputtered on two different substrates featuring substantial different hardness and Young´s modules (sapphire and SrTiO3) were studied. The microstructure and the mechanical properties such as hardness (H), Young´s modulus (E) and scratch parameters were investigated. The intrinsic hardness and Young´s modulus of YBCO thin films were found to be H ∼ 8.5 GPa, and E ∼ 210 GPa, respectively. The substrate´s influences on the mechanical parameters were found to be insignificant as long as the indentation penetration depth was below approximately 25% of the film thickness.