Superconducting properties of a 27-A<i></i>phase of Ba-Y-Cu-O

Abstract

High-purity (97%) samples of 27-A\r{} phase of Y-Ba-Cu-O have been prepared in superconducting thin films on (100) ${\mathrm{SrTiO}}_{3}$. The possibility that the observed superconductivity might arise from a residual 3% ${\mathrm{Ba}}_{2}$${\mathrm{YCu}}_{3}$${\mathrm{O}}_{7}$ impurity in this sample is ruled out using transmission electron microscopy which shows that it is present only as isolated particles. This allows for an unambiguous determination that the 27-A\r{} phase is superconducting with an onset ${T}_{c}$ of 82 K and ${T}_{c}$(R=0) of 79 K.