Deposition of superconducting Ba₂Ca_n-1Cu_nO_2n(O,F)₂ thin films by pulsed laser ablation

The highest ever superconducting critical temperature (T_c) of 120 K has been reported for the compound Ba₂Ca_n-1Cu_nO_2n(O,F)₂ (F-02(n-1)n). However, only bulk samples have been synthesized to date and extremely high pressures have been required. Here, the deposition of superconducting Ba₂Ca_n-1Cu_nO_2n(O,F)₂ films on a SrTiO₃(100) substrate was investigated using Nd-YAG pulsed laser ablation under an O₂ pressure of 16-19 Pa at a substrate temperature of 740-750 °C. The films exhibited a superconducting onset temperature (T_co) of 76.5 K and a zero resistance temperature (T_ce) of 22.5 K. The dominant diffraction peaks matched those reported for c-axis oriented Ba₂Ca₂Cu₂O₆(O,F)₂ (n = 3) bulk samples. However, the T_c values for the films were much lower than that for the bulk material, even though the ablation target composition was Ba₂Ca₂Cu₃O_6+δ(O,F)₂, which yields the highest bulk T_c value