Electron energy-loss spectroscopy study on relationship between oxygen deficiency sites and transition temperature of YBCO

Abstract The superconducting transition temperature ( T c ) in YBa 2 Cu 3 O 7− δ (YBCO) exhibits a nonlinear dependence on oxygen deficiencies. It is thought to be related to which oxygen sites are deficient, but details are unclear due to a lack of experimental data. In this study, we investigated the sites of oxygen deficiencies in YBCO thin films with varying T c using scanning transmission electron microscopy and electron energy loss spectroscopy. We found that deficiencies appear mainly at the Cu–O chain sites in T c ≈ 81 K and 64 K, while they appear at both Cu–O chain and CuO 2 planes sites in T c ≈ 49 K. We discussed why the transition temperature is constant around 60 K regardless of the amount of oxygen deficiencies (60 K plateau).