THE EFFECT OF OXYGEN CONTENT ON CRITICAL TEMPERATURE IN YBCO CUPRATE SUPERCONDUCTORS

YBa2Cu3O7−δ (YBCO) is one of the most intensively studied high-temperature cuprate superconductors because its superconducting transition temperature (Tc) is extraordinarily sensitive to oxygen stoichiometry. In this compound, the oxygen deficiency parameter δ controls both crystal symmetry and hole concentration in the CuO₂ planes that host superconductivity. As oxygen is removed from the Cu-O chain layer, charge transfer to the CuO₂ planes is reduced, the orthorhombic structure progressively transforms toward tetragonal symmetry, and Tc decreases in a distinctly non-linear manner [1-3]. Near full oxygenation, YBCO typically exhibits Tc values around 90-93 K, whereas strongly oxygen-deficient compositions become underdoped, weakly superconducting, or non-superconducting [1,4,5]. Oxygen ordering has an additional decisive role: samples with similar average oxygen content may display different superconducting behavior depending on vacancy arrangement and chain ordering [2,3]. This article reviews the structural, electronic, and superconducting consequences of oxygen variation in YBCO, with emphasis on the physical mechanisms linking oxygen content to carrier density, crystal symmetry, and superconducting phase stability. Common experimental approaches used to determine oxygen stoichiometry and Tc are also summarized. Overall, precise oxygen control remains essential for optimizing YBCO in both basic research and technological applications [1,6,7].

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