The oxygen-deficient orthorhombic oxide YBa2Cu3O 7-δ1-3 has been the centre of intense recent interest because of its bulk superconducting properties near 90 K. More recently the closely related oxide, La1.5Ba1.5Cu3O 7+δ, is receiving increased attention4-7. The yttrium analogue, Y1.5Ba1.5Cu3O 7+δ, has not been successfully synthesized by the usual ceramic routes involving firing at temperatures above 900°C8,9, because of its intrinsic metastability. Here we report on the synthesis and characterization of a majority (90-95%) phase Y1.5Ba 1.5Cu3O7+δ(referred to for historical reasons8 as Y 3-3-6), prepared by firing an atomically mixed citrate precursor between 810° and 825 °C for 2 h. X-ray powder diffraction data indicate that Y 3-3-6 is isostructural with its tetragonal La analogue4,7. Electron microprobe and thermogravimetry data yield a unit-cell composition Y(Ba2-xYx)Cu3O7+δ, with x=0.50 and δ=0.1-0.15 for the parent compound. Specimens of Y 3-3-6 with x = 0.50 and 0.375, which were annealed in O2 at 1 atm and >3 atm, displayed semiconducting behaviour. Filamentary superconductivity, detected electrically and magnetically, with transition onsets at 80 and 60 K respectively, is observed in specimens annealed in 3 atm O2 at 520°C.
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