Project

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Superconducting iron chalcogenides

English title Superconducting iron chalcogenides
Applicant Conder Kazimierz
Number 137870
Funding scheme Project funding
Research institution Paul Scherrer Institut
Institution of higher education Paul Scherrer Institute - PSI
Main discipline Inorganic Chemistry
Start/End 01.05.2012 - 30.04.2013
Approved amount 58'646.00
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All Disciplines (2)

Discipline
Inorganic Chemistry
Condensed Matter Physics

Keywords (4)

Supercoductivity; Iron superconductors; Chalcogenides; Single crystals

Lay Summary (English)

Lead
Lay summary

Superconducting iron chalcogenides

For fifteen years after discovery of High Temperature Superconductivity by G. Bednorz and K.A. Müller, complex oxides of copper seemed to be the only group of materials showing this property. The situation changed in 2001 after the discovery of superconductivity in MgB2 and more recently (2008) in Fe-based compounds. As polarized iron spins were assumed to break the Cooper pairs accountable for superconductivity, this last discovery was absolutely unexpected. Among the iron-based superconductors iron chalcogenides e.g. FeSe have the simplest layered structure. The superconducting transition temperature (Tc) of the iron selenide FeSe is only 8K but increases to about 14K when doped with Te and to over 30K under pressure or intercalated by alkali metal.

The following tasks will be performed within the frame of the project:

      1.Synthesis of AFeSe single crystals with isovalent (Te, S) and non-isovalent (P, Sb) dopant on anion site (A = K, Rb, Cs).

      2.Investigations of alkali metal intercalated AFeSe with Se sites substituted by Te, S, P or Sb and Fe sites substituted with Mn and Sm (A = K, Rb, Cs).

      3.Studies of possible intercalations of FeSe with alkali earth cations.

 

The obtained samples will be investigated using different methods: magnetization, specific heat, Hall and Seebeck effects and muon-spin-rotation spectroscopy. Detailed structural studies will be carried out by means of X-ray powder, synchrotron X-ray single crystal and neutron diffraction techniques.

The purpose of the work will be a search for an optimum composition/stoichiometry in respect of the superconducting properties and to provide a contribution to the understanding of the superconducting state in this materials, especially coexistence of magnetism and superconductivity.

Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Name Institute

Collaboration

Group / person Country
Types of collaboration
Laboratory for Neutron Scattering, PSI Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
Laboratory for muon Spectroscopy, PSI Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results

Associated projects

Number Title Start Funding scheme
141962 Mott Physics Beyond the Heisenberg Model in Iridates and Related Materials 01.01.2013 Sinergia

Abstract

The project is focused on detailed research and characterization of the new members of recently discovered iron-based HTc superconductors from AFe2Se2 122-family (A= K, Rb, Cs, Tl). These compounds are successors of FeCh superconductors (11 family, Ch = chalcogen atoms) with the most known representative FeSe1-x (Tc=8K). In 11-iron selenide superconductivity is realized having in the structure only “superconducting” layers with Fe cations tetrahedrally coordinated by Se. In the 122 superconducting iron chalcogenides alkali metals (or Tl) are intercalated between Fe-Se layers which rises Tc above 30K. All the studies performed up to now show that a right stiochiomety is crucial for superconducting properties. Additionally coexistence of the superconducting state with astonishing robust magnetism (TN~479 K) was observed. It seems to be possible to increase Tc by certain doping modifying electronic and/or structural properties. Within the frame of the project we plan to establish a possible range of stoichiometry of XyFe2-xSe2 (122 phase) as well as perform a detailed study of influence of crystal composition on their superconducting and magnetic properties. The samples will be investigated by means of magnetization, specific heat, thermal conductivity, Hall effect, Seebeck coefficient and muon-spin-rotation spectroscopy (µSR) measurements. Detailed structural investigations will be performed using X-ray powder, synchrotron X-ray single crystal and neutron diffraction. As the second goal synthesis of AFeSe crystals with isovalent (Te, S) and nonisovalent (P, Sb) dopant on anion site will be carried out followed by investigation of alkali metal intercalated AFe-Se, AFe-Se-Te, AFe-Se-S, AFe-Se-P, AFe-Se-Sb crystals with Fe substituted with Mn and Sm. In parallel we plan to perform the detailed studies of possible intercalations of the above systems with alkali earth cations (Ca, Sr, Ba). The proposed tasks are focused on expanding the materials science base for new HTc superconductors, identifying the property- structure-synthesis-chemistry relationships through advanced materials characterizations and developing the phase diagrams for the new iron-based superconducting compounds.
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