Superconductivity at 90 K in a multiphase oxide of Y-Ba-Cu

We have measured the resistance and dc susceptibility in a series of multiphase Y-M-Cu oxides, where M=Ca, Sr, and Ba. We find superconductivity in two of the Ba samples, of nominal composition Y_2-x{Ba}ₓCuO_4-y with x=0.20 and x=0.25 For x=0.25, the midpoint of the resistive transition is 91 K, the resistance has reached zero by 83 K, and the Meissner signal reaches 2% of that expected for an ideal bulk superconductor at low temperatures.