Preparation, structure, microwave absorption and other properties of the 125K superconductor Tl2Ca2Ba2Cu3O10+δ

It is shown that Tl2Ca2Ba2Cu3O10+δ (2223), the n=3 member of the Tl2O2. Can−1Ba2CunO2n+2 family shows a Tc (zero-resistance) of 125K (onset 140K) only when it is prepared by the sealed tube ceramic method starting from the 1313 composition. The structure is orthorhombic ( c ≈ 36 A ̊ compared to 30Å of 2122), but electron diffraction patterns show two possible orthorhombic structures. Lattice images show the expected local structure and also the presence of dislocations and intergrowths. Both 2223 and 2122 oxides absorb microwaves (9.1GHz) intensely in the superconducting state, with some hysteresis. XPS measurements show Cu mainly in the 1+ state, suggesting the important role of oxygen holes.