Defects that control the properties of Tl- and Hg-based superconductors

• Published in: Physica. C, Superconductivity Vol. 282; pp. 97 - 100
• Main Authors: Jorgensen, J.D., Chmaissem, O., Wagner, J.L., Jensen, W.R., Dabrowski, B., Hinks, D.G., Mitchell, J.F.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.08.1997
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/S0921-4534(97)00225-6

Defects that affect T c in Tl 2Ba 2CuO 6+δ and HgBa 2CuO 4+δ have been characterized by neutron powder diffraction. In Tl 2Ba 2CuO 6+δ, the dominant defect is interstitial oxygen between the two TlO planes, but Cu substitution on the Tl site also affects properties and there is evidence for a second oxygen defect for compositions in the vicinity of maximum T c. In HgBa 2CuO 4+δ, there are two competing oxygen defects in the Hg layer. The relative concentrations of these defects switches upon passing from the underdoped region, through the maximum T c, to the overdoped region. This remarkable behavior could result from a change in the topology of the Fermi surface upon passing through the van Hove singularity.