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Synthesis and properties of substituted Hg-based superconductors
Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
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.
Keyword [en]
Hg-based cuprate superconductors, synthesis and structure determination, LiF flux, oxyfluorides, irrevrsibility line
National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:su:diva-246ISBN: 91-7265-918-1 (print)OAI: oai:DiVA.org:su-246DiVA: diva2:191464
Public defence
2004-10-07, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 12 A, Stockholm, 14:00
Opponent
Supervisors
Available from: 2004-09-16 Created: 2004-09-16Bibliographically approved
List of papers
1. Synthesis and investigation of (Hg1-xCux)Ba2Ca2Cu3O8+δ
Open this publication in new window or tab >>Synthesis and investigation of (Hg1-xCux)Ba2Ca2Cu3O8+δ
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2002 In: Physica C, ISSN 0921-4534, Vol. 366, no 4, 263–269- p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-23340 (URN)
Note
Part of urn:nbn:se:su:diva-246Available from: 2004-09-16 Created: 2004-09-16Bibliographically approved
2. Investigation of LiF flux influence on HgBa2CaCu2O6+δ synthesis
Open this publication in new window or tab >>Investigation of LiF flux influence on HgBa2CaCu2O6+δ synthesis
2004 In: Materials Research Bulletin, ISSN 0025-5408Article in journal (Refereed) Submitted
Identifiers
urn:nbn:se:su:diva-23341 (URN)
Note
Part of urn:nbn:se:su:diva-246Available from: 2004-09-16 Created: 2004-09-16Bibliographically approved
3. Enhancement of Tc in HgBa2Ca2Cu3O8+δ by fluorination
Open this publication in new window or tab >>Enhancement of Tc in HgBa2Ca2Cu3O8+δ by fluorination
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2001 In: Physical Review B, ISSN 1098-0121, Vol. 63, no 6, 064511- p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-23342 (URN)
Note
Part of urn:nbn:se:su:diva-246Available from: 2004-09-16 Created: 2004-09-16Bibliographically approved
4. Fluorinated Hg-1223 under pressure: the ultimate Tc of the cuprates?
Open this publication in new window or tab >>Fluorinated Hg-1223 under pressure: the ultimate Tc of the cuprates?
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2004 (English)In: Physica. C, Superconductivity, ISSN 0921-4534, Vol. 408-410, 23-24 p.Article in journal (Refereed) Published
Abstract [en]

High pressure experiments have revealed that Tc is affected by two main pressure-dependent parameters: the doping level of the CuO2 planes and by an intrinsic factor. The origin of the intrinsic factor is still unclear as, depending on the experiment, it is associated with the reduction of the c or the a lattice parameters. F incorporation into the Hg-1223 structure yields an enhancement of Tc up to a susceptibility onset of 138 K, mainly related to a compression of the a crystallographic axis. We have obtained a new high Tc record (166 K ± 1.5 K) by applying pressure (23 GPa) in the fluorinated Hg-1223 superconductor optimally doped. Tc increases with increasing pressure, reaching different maximum values, depending on the F doping level, and decreases for a further increase of pressure. This saturation of Tc may be the highest Tc that can be obtained for the cuprates, considering the particular structural characteristics of this system.

Place, publisher, year, edition, pages
Elsevier B.V, 2004
Keyword
Pressure effects; Cuprates; Fluorinated Hg-1223
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-23343 (URN)10.1016/j.physc.2004.02.020 (DOI)
Note
Part of urn:nbn:se:su:diva-246Available from: 2004-09-16 Created: 2004-09-16 Last updated: 2010-10-04Bibliographically approved
5. Temperature behaviour of irreversibility fields of various Hg-based superconducting ceramics
Open this publication in new window or tab >>Temperature behaviour of irreversibility fields of various Hg-based superconducting ceramics
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2002 In: Physica C, ISSN 0921-4534, Vol. 372-376, no 3, 1865–1867- p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-23344 (URN)
Note
Part of urn:nbn:se:su:diva-246Available from: 2004-09-16 Created: 2004-09-16Bibliographically approved
6. Irreversibility fields of the high-Tc superconductors Hg-1212 and (Hg,Tl)-1212
Open this publication in new window or tab >>Irreversibility fields of the high-Tc superconductors Hg-1212 and (Hg,Tl)-1212
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2003 In: Physica C, ISSN 0921-4534, Vol. 391, no 3, 298–304- p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-23345 (URN)
Note
Part of urn:nbn:se:su:diva-246Available from: 2004-09-16 Created: 2004-09-16Bibliographically approved
7. Magnetic investigations of the high-Tc superconductor Hg-1212
Open this publication in new window or tab >>Magnetic investigations of the high-Tc superconductor Hg-1212
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2003 In: Physica C, ISSN 0921-4534, Vol. 388-389, 247–248- p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-23346 (URN)
Note
Part of urn:nbn:se:su:diva-246Available from: 2004-09-16 Created: 2004-09-16Bibliographically approved

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