Recent progress in Hg-based cuprates
- Swiss Federal Inst. of Technology, Zurich (Switzerland). Lab. fuer Festkoerperphysik
The recent discovery of superconductivity in HgBa{sub 2}CuO{sub 4 + {delta}} below 94K suggested the possibility of considerably enhanced critical temperatures {Tc} in similar compounds with more than one Cu-O plane per unit cell of the crystal lattice. Attempts to synthesize the compounds HgBa{sub 2}Ca{sub n{minus}1}Cu{sub n}O{sub 2n+2+{delta}} with n = 2, 3 or 4 (Hg 1212, Hg 1223 and Hg 1234) have been successful and maximum values of {Tc} exceeding 130K have been achieved. Both x-ray and neutron-diffraction techniques have been used to investigate the structural aspects of these materials. High-resolution electron microscopy revealed the existence of perfectly ordered polytypes, formed by stockings of Hg 1212 and Hg 1223 unit cells along the c direction; corresponding c-axis constants of up to 188 {angstrom} have been evaluated. The bulk character of superconductivity was verified by specific-heat experiments, revealing c{sub p}(T) anomalies accompanying the phase transitions. These data suggest again considerable fluctuation effects above {Tc}, as previously found by various experimental techniques in other high-{Tc} cuprates. The temperature dependence of the excess specific heat just below {Tc} seems less {lambda}-like than reported for some of the other superconducting copper oxides. Variations of the critical temperature by changing external parameters have been established. Replacing Hg by Pb and/or Oxygen annealing lead to changes of {Tc} of more than 10%. Some results obtained for Pb-substituted Hg-1223 compounds suggest that this series is the first example of cuprates containing 3 Cu-O layers in which the doping level may continuously be tuned from an underdoped to overdoped situations. Band-structure calculations indicate that Hg-0 derived electron bands may lead to self-doping effects in Hg-1223. The maximum value for {Tc} obtained by varying the chemical composition lead to a maximum {Tc} of 134.3K. Application of external pressure enhances {Tc}.
- OSTI ID:
- 64704
- Report Number(s):
- CONF-940142-; ISBN 0-8194-1453-0; TRN: IM9528%%364
- Resource Relation:
- Conference: OE/LASE `94: conference on optics, electro-optics, and laser applications in science and engineering, Los Angeles, CA (United States), 22-29 Jan 1994; Other Information: PBD: 1994; Related Information: Is Part Of Oxide superconductor physics and nano-engineering. Proceedings SPIE Volume 2158; Pavuna, D.; Bozovic, I. [eds.]; PB: 281 p.
- Country of Publication:
- United States
- Language:
- English
Similar Records
Effects of 1-MeV proton irradiation in Hg-based cuprate thin films
Synthesis and characterization of single crystals of the superconductors Hg{sub 0.8}Bi{sub 0.2}Ba{sub 2}Ca{sub {ital n}{minus}1}Cu{sub {ital n}}O{sub 2{ital n}+2+{delta}} ({ital n}=2,3)