New oxyfluoride superconductors Sr2Can-1CunO2n+δF2±y (n = 2; Tc = 99 K, n = 3; Tc = 111 K) prepared at high pressure

Article abstract of DOI:10.1016/0921-4534(95)00777-6

We prepared new oxyfluoride superconductors, Sr₂CaCu₂O_4+δF_2±y and Sr₂Ca₂Cu₃O_6+δF_2±y, at 1250 °C under 5.5 GPa. These phases are the n = 2, 3 members of a homologous series, Sr₂Ca_n-1Cu_nO_2n+δF_2±y, respectively, in which the n = 1 phase was reported previously. X-ray and HRTEM studies indicated that they have tetragonal structures with a = 3.843(1), c = 19.88(1) angstroms for n = 2 and a = 3.840(1), c = 26.17(1) angstroms for n = 3. The n = 2 phase showed a superconducting transition at 99 K, while the n = 3 one at 111 K.