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Magnetic investigations of the high-Tc superconductor Hg-1212
Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
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2003 In: Physica C, ISSN 0921-4534, Vol. 388-389, 247–248- p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
2003. Vol. 388-389, 247–248- p.
URN: urn:nbn:se:su:diva-23346OAI: diva2:191463
Part of urn:nbn:se:su:diva-246Available from: 2004-09-16 Created: 2004-09-16Bibliographically approved
In thesis
1. Synthesis and properties of substituted Hg-based superconductors
Open this publication in new window or tab >>Synthesis and properties of substituted Hg-based superconductors
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is focused on studies of substituted Hg-based superconducting copper oxides ((Hg1-xMx)Ba2Can-1CunO2n+2+δ). These compounds are promising objects of investigation, not only from a fundamental point of view but also because of their high values of superconducting transition temperature (Tc) and irreversibility field (Hirr).

The first part of the thesis is devoted to optimization of the synthesis procedure for Hg-based cuprates. The influence of different parameters (T, t, p(Hg), p(O2)) on the synthesis of these compounds in sealed silica tubes was studied. Optimal conditions yielded samples containing up to 95% of HgBa2Ca2Cu3O8+δ (Hg-1223). The formation of solid solutions with the formula (Hg1-xCux)Ba2Ca2Cu3O8+δ (where x <= 0.5) was also established. Another technique was developed, using LiF as a flux, for synthesis of samples containing up to 90% of the HgBa2CaCu2O6+δ (Hg-1212) phase.

The second part concerns synthesis and studies of oxyfluorides using Hg-1212 and Hg-1223 as starting materials together with XeF2 as a fluorinating agent. It was found that oxyfluorides of both phases have a parabolic dependence of Tc vs. a parameter as well as enhanced Tc values (ΔT ≈ 3-4 K) in comparison with optimally doped non-fluorinated analogues. The crystal structure of Hg-1223 oxyfluoride was studied by X-ray powder and neutron diffraction methods. It is suggested that chemical modification of the crystal structure leads to a decrease in Cu-O distance without noticeable change in Cu-O-Cu angle (in the (CuO2) layers), which may be the significant factors influencing this Tc increase. Hg-1223 oxyfluoride was also studied under high pressure for first time. It was found that this compound has a record-high Tc value (≈ 166 K) at P ≈ 23 GPa.

The last part describes the investigation of substituted Hg-based superconductors in the series (Hg0.9M0.1)Ba2CuO4+δ {(Hg,M)-1201}, where M = Tl, Pb, W, Mo, Nb and V. A comprehensive study of these compounds by various methods (X-ray powder diffraction, EDX, IR-, EXAFS- and XANES -spectroscopy) indicated that the change of charge carrier doping level is a crucial factor determining the irreversibility line. (Hg0.9Mo0.1)Ba2CuO4+δ showed the most improved irreversibility line position among the (Hg,M)-1201 compounds studied in this series.

Place, publisher, year, edition, pages
Stockholm: Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi, 2004. 76 p.
Hg-based cuprate superconductors, synthesis and structure determination, LiF flux, oxyfluorides, irrevrsibility line
National Category
Inorganic Chemistry
urn:nbn:se:su:diva-246 (URN)91-7265-918-1 (ISBN)
Public defence
2004-10-07, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 12 A, Stockholm, 14:00
Available from: 2004-09-16 Created: 2004-09-16Bibliographically approved

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