THE 2201 THALLIUM CUPRATE - TCS UP TO 92-K CAN BE ACHIEVED BY HYDROGEN ANNEALING

Polycrystalline tetragonal superconductors Tl2Ba2CuO6±δ with critical temperatures ranging from 12 K to 92 K were synthesized by combining two techniques, synthesis in evacuated ampoules and annealing in an H2/Ar flow at 290°C. It is demonstrated that several tetragonal forms exhibit bulk superconductivity with diamagnetic volume fractions ranging from 25% to 65%, whereas other tetragonal forms do not superconduct. However, results obtained for the orthorhombic samples suggest that this material does not superconduct. These results show that two factors play an important role in the appearance of superconductivity in the thallium cuprates: the oxygen nonstoichiometry, which governs the hole carrier density, and the homogeneous distribution of the oxygen and vacancies, which should improve superconductivity. Relationships between structure, chemical bonding and superconductivity in Tl2Ba2CuO6±δ are also discussed. © 1990.