Formation of epitaxial Tl₂Ba₂Ca₂Cu₃O₁₀ superconducting films by dc-magnetron sputtering and triple post-annealing method

For obtaining pure phase Tl₂Ba₂Ca₂Cu₃O₁₀ (Tl-2223) films with good superconducting properties, the growth technique is improved by dc magnetron sputtering and a triple post-annealing process. The triple post-annealing process comprises annealing twice in argon and once in oxygen at different temperatures. In the first low-temperature annealing phase in argon, Tl₂Ba₂CaCu₂O₈ (Tl-2212) is obtained to effectively minimize evaporation in the next step. With the increase of temperature in the second annealing stage in argon, the previously prepared Tl-2212 inter-phase is converted into Tl-2223 phase. An additional annealing in oxygen is also adopted to improve the properties of Tl-2223 films, each containing an optimal oxygen content value. The results of X-ray diffraction (XRD) θ -2θ scans, ω scans and rotational ø scans show that each of the Tl-2223 films has a high phase purity and an epitaxial structure. Smooth films are observed by scanning electron microscopy (SEM). The critical temperatures T_c of the films are measured to be about 120 K and the critical current densities J_c can reach 4.0 MA/cm² at 77 K at self field.