Atomic disorder in low pressure rf-sputtered YBCO superconducting thin films

The epitaxial films of YBCO grown by low pressure (∼ 10 −3 Torr) rf-magnetron sputtering, exhibiting ‘c’- axis lattice parameter 11.753 A and 11.718 A on MgO(100) and SrTiO 3 (100), respectively, were subjected to the Rutherford backscattering technique (RBS) for their compositional analysis. The backscattering-simulations performed on these films have revealed a gradient in the concentration of both Ba and Cu cations across the thickness of the film. The cation ratios (Ba:Y and Cu:Y) in the films grown on different substrates are found to be substrate dependent. In this paper, an attempt has been made to correlate the observed cation deficiencies with the employed experimental conditions. It is conjectured that the observed cation deficiency is expected to give rise to ‘Y-for-Ba’ replacement, thereby resulting in the extension of the c -axis parameter. This atomic disorder (replacement) also explains the observed lower values of T c .