Structure, Resistivity, Critical Field, Specific-Heat Jump at T c , Meissner Effect, a.c. and d.c. Susceptibility of the High- T c 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 T_c are consistent with γ 2 mJ/(K² gat) (9 mJ/(K² mole-Cu)), neglecting all renormalizations.