Submicrometer Superconducting YBa 2 Cu 3 O 6+x Particles Made by a Low-Temperature Synthetic Route

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Abstract
Evidence suggests that superconducting, orthorhombic YBa2Cu3O6+x+ (x ≳ 0.5) is always produced by oxidation of the oxygen-deficient, tetragonal form (x ≲ 0.5) of this phase (commonly referred to as 123). A synthetic route whereby solution-derived, carbon-free precursors are decomposed at 650° to 700°C in inert atmosphere to yield tetragonal 123 is now available. Appropriate precursors include hydrated oxides derived from the hydrolysis of organometallic solutions and aqueous solution-derived hyponitrites. Subsequent oxidation of the tetragonal phase at 400°C results in submicrometer particles of orthorhombic 123. Superconductivity (Tc onset ≈87 K) has been confirmed in these materials by both Meissner effect and specific-heat measurements.