Thickness dependence of microcrack formation in YBa2Cu3O6Â +Â x thin films on NdGaO3 (001) substrates

Thickness dependence of parallel microcrack formation in YBa2Cu3O6 + x thin films prepared by pulsed laser deposition from nano- (n) and microcrystalline (μ) targets on NdGaO3 (001) is systematically investigated. Atomic force microscope and x-ray diffraction measurements show parallel microcracks normal to uniaxial twin boundaries. The amount of microcracks increases with film thickness. Superconducting properties of the films decrease very strongly with film thickness as a result of microcrack formation. The n-films have more rigid lattice and thus show more extensive cracking than μ-films. It is found that the μ-films have a thickness threshold (∼ 70 nm) where the first signs of cracking appear.