Nanoindentation of multilayered epitaxial YBa2Cu3O7-δ thin films and coated conductors

Nanoindenter tests were carried out on YBa2Cu3O7-δ (YBCO) coatings with different buffer layers, in order to obtain the Hardness (H) tendency, Young's modulus (E), and the fracture mechanism activated during the indentation process. Different pop-ins were observed in the load–displacement curves, and correlated with their residual nanoindentation imprints visualized by Atomic Force Microscopy. A trench was made by Focused Ion Beam in order to better understand the plastic behaviour activated under the residual imprint at 650 mN of applied load. During the first steps of nanoindentation experiments an elastic regimen takes place and the Hertzian equations can be applied to obtain the E for each YBCO coating. All YBCO coatings present similar E values and H tendencies. However, the YBCO/CeO2/Yttrium Stabilized Zirconia system exhibits a better mechanical stability probably due to the absence of microcracks under the indentation. In addition, an experimental process using nanoindentation technique is obtained in order to isolate the kind of buffer layer employed (single crystal substrate or metallic substrate).