Fabrication of Tl₂Ba₂CaCu₂O₈ superconducting films without thallium pellets

A new improved two-step method in fabricating Tl₂Ba₂CaCu₂O₈ (Tl-2212) thin films is presented in this paper. In the first process of dc magnetron sputtering, the thallium content in the precursor film is largely increased by adjusting the ratio of thallium in the sputtering targets. After the second annealing process in the absence of additional thallium pellets or powder source, high-quality Tl-2212 thin films can be obtained. The proper content of thallium in the precursor film provides a relatively stable atmosphere to guarantee the growth of Tl-2212 film. This method avoids the repeated production of the thallium pellets in the post-annealing process, the repeatability and controllability of the experiment are greatly improved. X-ray diffraction (XRD) scans show that all of the sharp peaks of the sample films can be assigned to the (00l) peaks of Tl-2212 phase. The highest superconducting critical temperature (T_c) of the films is 105 K and the critical current density (J_c) can achieve 1.93 MA/cm² in zero magnetic field at 77 K for a 600 nm film.