NICOP - Deciphering the workings of molecule intercalated iron chalcogenides
Abstract
The layered iron-chalcogenide ~-Fe1+yCh (Ch= S, Se), has attracted great attention as itshows an 8 K superconducting transition (Tc"") at ambient pressure. Favourably, intercalationof electron donating spacers (A) between the FeCh sheets raises the Tc up to 30 K i""nAxFe2Se2 type of compounds. However, their high-temperature synthesis is accompanied byunwanted microscale phase-separation. Thus"", in order to understand superconductivity in thisfamily of materials we must tackle the subtle stoichiometry required to attain a" sizeable Tc.The research thrusts that motivate this project entail devising alternative chemical pathwaysfor single-phase materials and based on them to parameterize the conditions leading to Tcenhancement. The new iron-chalcogenides produced through this work" will be a vehicle forunderstanding fundamental questions, namely in what way (i) the separation of theneighbouring FeCh layers is"" essential before Tc is saturated (~45 K), (ii) the doping of theFeCh sheets together with other factors, such as the Fe-Ch coordin"ation or the FeChmagnetism could engineer the value and evolution of Tc beyond its current limitations.We will develop low-tempera"ture, solvothermal routes to examine the broader applicabilityof the intercalation phenomenon that promotes the FeCh interlayer sep""aration, while Tc ismanipulated chemically. The intercalation chemistry of FeCh layers (host) will be pursuedwith selected types o""f organic molecules (guests) that will act as solvents for the alkali metals(A= Li, Na etc). We propose to explore how the solvents"~ (chosen from the family of amines)increasing electron donating capability may be a controlling factor for intercalating FeCh thus"allowing single-phase isolatable complexes of the Ax(solvent)Fe2-zCh2 type.As ex situ growth may miss low-temperature, nonequilibr""ium products, we offer toimplement in situ high-throughput diffraction monitoring to identify the phase diagram ofnew iron-chalcog"enide intercalates far below the temperatures of traditional solid-statereactions. Access (via peer-reviewed proposals) to DOE user#NAME?"s of such endeavors. The outputs will feed back ex situ synthetic protocols for singlephasehyper-expanded lattice compounds, and co"mplement computational theory efforts forpredictive understanding of structure-property relationships.Enhancements or depressions of Tc noted in these materials will be assessed in view ofchemical protocols promoting charge transfer between electron donating i"ntercalates and theFeCh host. As modifications upon doping occur at variable length and time scales, neutronscattering will be ins"trumental for resolving the subtle structural/magnetic correlations thatinfluence how the intraplanar electron-pairing is establish"ed.We envisage that the proposed organic-inorganic superconductors could offer a simple, costefficientmaterials design approach to"" ~program~ the strength of the electron-pairing(~2~/kBTc, where ~ is the superconducting energy gap) by optimising the host-guesti"nteraction with chemically versatile intercalates. Tuning the superconducting energy gap(sub-THz and THz spectral regions) renders such materials good candidates for technologicalapplications in the far-IR and/or millimeter-wave bands. Fe-chalcogenides could then offer along-term solution for increased reliability communication and surveillance electronics ofpotential interest to the Elec"tromagnetic Maneuver Warfare focus area of the Naval S&TStrategy. Apart from this principal focus, the aforementioned concepts may" also play a keyrole in the development of complementary power-saving components that could meet theemerging requirements of ONR~s program for Energy security and self-sufficiency.The challenges set out here will be tackled through a collaborative initiative be"tweenEuropean (Foundation for Research and Technology, Greece & Warsaw University ofTechnology, Poland) and US scientists (Brookha""ven National Lab, NY & NHMFL, FL). Acomprehensiv
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Sep 29, 2017
- Source ID
- N629091712126
Entities
People
- Alexandros Lappas
Organizations
- Foundation for Research and Technology – Hellas
- Office of Naval Research
- United States Navy