Observation of a halide (F/Cl) stabilized, new perovskite phase in superconducting Y2Ba5Cu7Ox films

Abstract

A new, ordered perovskite structure was stabilized as a majority phase in superconducting Y₂Ba₅Cu₇O_20−δ’(F/Cl)_δ‘ films epitaxially grown on SrTiO₃(100). The new phase was formed via fluorination or chlorination introduced during the post‐deposition O₂ furnace anneal for recrystallization. The structure is determined by x‐ray diffraction to be an orthorhombic unit cell [a∼b=3.86(1) Å, c=27.24(6) Å] with reflection conditions consistent with a fully twinned A‐centered cell. Films containing primarily the new phase show a lower resistivity ρ(300 K)∼177 μΩ cm, a comparable ratio of ρ(300 K)/ρ(100 K)∼3.0, and a lower superconducting temperature of 78–74 K when compared to Y₁Ba₂Cu₃O₇.