Superconducting selenides intercalated with organic molecules: synthesis, crystal structure, electric and magnetic properties, superconducting properties, and phase separation in iron based-chalcogenides and hybrid organic-inorganic superconductors

Abstract

Layered iron-based superconducting chalcogenides intercalated with molecular species are the subject of intensive studies, especially in the field of solid state chemistry and condensed matter physics, because of their intriguing chemistry and tunable electric and magnetic properties. Considerable progress in the research, revealing superconducting inorganic-organic hybrid materials with transition temperatures to superconducting state, T , up to 46 K, has been brought in recent years. These novel materials are synthesized by low-temperature intercalation of molecular species, such as solvates of alkali metals and nitrogen-containing donor compounds, into layered FeSe-type structure. Both the chemical nature as well as orientation of organic molecules between the layers of inorganic host, play an important role in structural modifications and may be used for fine tuning of superconducting properties. Furthermore, a variety of donor species compatible with alkali metals, as well as the possibility of doping also in the host structure (either on Fe or Se sites), makes this system quite flexible and gives a vast array of new materials with tunable electric and magnetic properties. In this review, the main aspects of intercalation chemistry are discussed with a particular attention paid to the influence of the unique nature of intercalating species on the crystal structure and physical properties of the hybrid inorganic-organic materials. To get a full picture of these materials, a comprehensive description of the most effective chemical and electrochemical methods, utilized for synthesis of intercalated species, with critical evaluation of their strong and weak points, related to feasibility of synthesis, phase purity, crystal size and morphology of final products, is included as well.

Tuning Fe–Se Tetrahedral Frameworks by a Combination of [Fe(en)3]2+ Cations and Cl– Anions

“…Clarke et al reported the first reliable crystal structure determination of Li-ammonia intercalate in FeSe with T c as high as 43 K, as well as in situ characterization of the reactions of Li/NH 3 with FeSe using X-ray and neutron diffraction . Insertion of transition metal coordination complexes with bulky ligands between the Fe chalcogenide layers allows further expansion of the interlayer space , and contributes in tuning interactions of Fe-amine complexes with chalcogenide fragments. − Ethylenediamine ( en ) has been widely used as both a bidentate ligand and a solvent in the synthesis of such materials due to its versatility, high tendency to coordinate with transition metals, and compatibility with Fe-based chalcogenides. − …”

Lix(C5H5N)yFe2–zSe2: A Defect-Resilient Expanded-Lattice High-Temperature Superconductor

“…Except simple metal cations, solvates of selected alkali or alkaline-earth metals with bases (cf. ammonia, aliphatic amines, diamines, and aromatic amines) comprise another type of intercalating species that can enter the structure of β-FeSe as electron donors that further promote T c enhancement . Interestingly, in these types of iron chalcogenide intercalates, there is a correlation of the interlayer spacing ( d , defined as the Fe–sheet distance in adjacent FeSe layers, along the c axis) with T c , which empirically shows a progressive growth of T c with increasing d that saturates at a separation of d ∼ 8.6 Å .…”

Electrochemical Synthesis and Crystal Structure of the Organic Ion Intercalated Superconductor (TMA)0.5Fe2Se2 with Tc = 43 K

“…22 However, intercalation reactions with β-FeSe as host compound can proceed at low temperatures via soft chemistry methods. [23][24][25][26][27] Examples are the intercalation of lithium ions together with amine and amide species in liquid ammonia (Li x (NH 2 ) y (NH 3 ) 1−y Fe 2 Se 2 , T c = 43 K), 28 of lithium hydroxide layers ([(Li 1-x Fe x )OH]FeSe, T c = 42 K) 29 by hydrothermal methods, or of alkaline ions with amine molecules (Na 0.39 (C 2 N 2 H 8 ) 0.77 Fe 2 Se 2 T c = 46 K) by solvothermal reactions. 26 Another promising approach is the electrochemical intercalation of alkali metal ions.…”

“…However, intercalation reactions with β-FeSe as host compound can proceed at low temperatures via soft chemistry methods. − Examples are the intercalation of lithium ions with amine and amide species in liquid ammonia (Li x (NH 2 ) y (NH 3 ) 1– y Fe 2 Se 2 , T c = 43 K), lithium hydroxide layers by hydrothermal methods ([(Li 1– x Fe x )­OH]­FeSe, T c = 42 K), or alkaline ions with amine molecules by solvothermal reactions (Na 0.39 (C 2 N 2 H 8 ) 0.77 Fe 2 Se 2 , T c = 46 K) …”