First evidence of natural superconductivity: covellite

Benedetto, Francesco Di; Borgheresi, M.; Caneschi, Andréa; Chastanet, Guillaume; Cipriani, Curzio; Gatteschi, Dante; Pratesi, Giovanni; Romanelli, Marco; Sessoli, Roberta

doi:10.1127/0935-1221/2006/0018-0283

Cited by 53 publications

(35 citation statements)

References 18 publications

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“…The low intensity of the magnetic shielding (4%) leaves the question open, whether superconductivity occurs in the bulk or locally at the surface and/or in some small, granular and not connected volume. The observed transition cannot be due to any secondary phase or non reacted precursors: among them, pure Bi can only become superconducting under pressure, and CuS is superconducting below 1.6 K [9]. The field cooled susceptibility is 1.6%, providing the strongest evidence for superconductivity below 5.8 K. A superconducting hysteresis loop opens in m(H) measurements and is shown in Fig.3.…”

Section: Resultsmentioning

confidence: 98%

BiOCuS: A new superconducting compound with oxypnictide-related structure

Ubaldini

Giannini

Senatore

et al. 2010

Physica C: Superconductivity and its Applications

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The discovery of about 50 K superconductivity in the tetragonal Fe-based pnictides has stimulated the search for superconductivity in a wide class of materials with similar structure. Copper forms compounds isostructural to LaOFeAs. Single phase BiOCuS can be prepared by a solid state reaction at temperature lower than 500 • C from a mixture of Bi 2 O 3 , Bi 2 S 3 and Cu 2 S. The samples have been characterized by means of EDX analysis, X-ray diffraction, magnetic and electrical measurements. The cell parameters are a = 3.8708 Å, c = 8.565 Å. Charge carrier doping can be realized either by F substitutions for O, or by Cu off-stoichiometry. The latter doping route leads to the occurrence of superconductivity below T c = 5.8 K.

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Section: Resultsmentioning

confidence: 98%

BiOCuS: A new superconducting compound with oxypnictide-related structure

Ubaldini

Giannini

Senatore

et al. 2010

Physica C: Superconductivity and its Applications

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“…However, XANES and X-ray photoelectron spectroscopy (XPS) data show little evidence for Cu(II) in covellite [44,45], reflecting the covalent nature of the Cu-S bonds and the mainly monovalent nature of Cu in this mineral.…”

Section: +mentioning

confidence: 99%

Distribution and Substitution Mechanism of Ge in a Ge-(Fe)-Bearing Sphalerite

et al. 2015

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Abstract:The distribution and substitution mechanism of Ge in the Ge-rich sphalerite from the Tres Marias Zn deposit, Mexico, was studied using a combination of techniques at μm-to atomic scales. Trace element mapping by Laser Ablation Inductively Coupled 118Mass Spectrometry shows that Ge is enriched in the same bands as Fe, and that Ge-rich sphalerite also contains measurable levels of several other minor elements, including As, Pb and Tl. Micron-to nanoscale heterogeneity in the sample, both textural and compositional, is revealed by investigation using Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) combined with Synchrotron X-ray Fluorescence mapping and High-Resolution Transmission Electron Microscopy imaging of FIB-prepared samples. Results show that Ge is preferentially incorporated within Fe-rich sphalerite with textural complexity finer than that of the microbeam used for the X-ray Absorption Near Edge Structure (XANES) measurements. Such heterogeneity, expressed as intergrowths between 3C sphalerite and 2H wurtzite on [11 0] zones, could be the result of either a primary growth process, or alternatively, polystage crystallization, in which early Fe-Ge-rich sphalerite is partially replaced by Fe-Ge-poor wurtzite. FIB-SEM imaging shows evidence for replacement supporting the latter. Transformation of sphalerite into wurtzite is promoted by (111)* twinning or lattice-scale defects, leading to a heterogeneous ZnS sample, in which the dominant component, sphalerite, can host up to ~20% wurtzite. Ge K-edge XANES spectra for this sphalerite are identical to those of the germanite and argyrodite standards and the synthetic chalcogenide glasses GeS2 and GeSe2, indicating the Ge formally exists in the tetravalent form in this sphalerite. Fe K-edge XANES spectra for the same sample indicate that Fe is present mainly as Fe 2+, and Cu K-edge XANES spectra are characteristic for Cu + . Since there is no evidence for coupled substitution involving a monovalent element, we propose that Ge ) with vacancies in the structure to compensate for charge balance. This study shows the utility of synchrotron radiation combined with electron beam micro-analysis in investigating low-level concentrations of minor metals in common sulfides.

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“…Most of the copper sulphide phases such as Cu 2 À x S (digenite), Cu 1.96 S (djurleite), Cu 1.75 S (anilite) and CuS (covellite) show a semiconducting behaviour. The covellite CuS shows excellent metallic conductivity and transforms to type-I superconductor at 1.6 K [2]. Covellite CuS has attracted growing attention in recent years due to their excellent physical and chemical properties.…”

Section: Introductionmentioning

confidence: 99%