Structure, Resistivity, Critical Field, Specific-Heat Jump at <i> T _c </i> , Meissner Effect, a.c. and d.c. Susceptibility of the High- <i> T _c </i> Superconductor YBa ₂ Cu ₃ O ₇

Abstract

YBa2Cu3O7 superconductors with inductive transitions as narrow as 0.45 K above 90 K were synthetized. Samples were characterized by thermogravimetry, differential thermal analysis, X-ray and neutron diffraction. The structure is characterized by a two-dimensional Cu-O network with square-pyramidal and square-planar coordinated Cu atoms. Results show a clear metallic behaviour of the resistivity. An orbital critical field as high as 300 T is extrapolated. Meissner flux expulsion up to 40% is observed. Small amounts of magnetic Cu2+ ions are correlated with the presence of the impurity phase BaCuO2. The Pauli susceptibility and the specific-heat jump at Tc are consistent with γ ≃ 2 mJ/(K2 gat) (9 mJ/(K2 mole-Cu)), neglecting all renormalizations.