Effect of fluorination and high pressure on the structure and properties of the Hg-bearing superconducting Cu mixed oxides

• Published in: Physica. C, Superconductivity Superconductivity, 2000-08, Vol.338 (1-2), p.52-59
• Main Authors: Putilin, S.N, Antipov, E.V, Abakumov, A.M, Rozova, M.G, Lokshin, K.A, Pavlov, D.A, Balagurov, A.M, Sheptyakov, D.V, Marezio, M
• Format: Article
• Language: English
• ISSN: 0921-4534
• DOI: 10.1016/S0921-4534(00)00201-X

The T sub(c) variation of HgBa sub(2)CuO sub(4+ delta ) (Hg-1201) and HgBa sub(2)CuO sub(4)F sub( delta ) can be achieved by a change in the carrier concentration and by a compression of the structure under high pressure. Oxygenated and fluorinated series exhibit a cupola-shaped behavior for the T sub(c) vs. delta dependence, but the curves are shifted away from each other along the delta axis. NPD showed double amount of extra fluorine in comparison with extra oxygen for the oxygenated Hg-1201 phases with close T sub(c)'s. An exchange of the extra oxygen by a double amount of fluorine causes a significant compression of the apical Cu-O bond distances, while the in-plane ones, as well as T sub(c), do not vary. Fluorination of Hg-1223 resulted in a slight increase in T sub(c) in comparison with oxygenated material. The influence of the external pressure on the structure and T sub(c) of Hg-1201 strongly depends on the doping level. An increase in the extra oxygen content from underdoped to overdoped state results in the larger compression of the apical Cu-O and Ba-O sub(Hg) distances while the HgO sub(2) dumbbell as well as a distance between Ba and O from the (CuO sub(2)) layers become practically pressure independent.