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Superconductivity in a 122-type Fe-based compound (La,Na,K)Fe₂As₂.

ABSTRACT: We synthesized a Fe-based superconductor (FeSC), (La,Na,K)Fe₂As₂, and characterized its superconducting properties. It was found that (La,Na,K)Fe₂As₂ has a 122-type (ThCr₂Si₂-type) structure with a space group I4/mmm (No. 139), identical to (Ba,K)Fe₂As₂ and (La,Na)Fe₂As₂ but distinct from so-called 1144-type FeSCs such as CaKFe₄As₄ and (La,Na)CsFe₄As₄. The results demonstrate that the formation of the 1144-type phase necessitates the large ionic radius mismatch among the so-called A-site constituent elements of the AFe₂As₂ formula. The lattice constants are a = 3.850(1) Å and c = 13.21(1) Å. The La, Na, and K ions occupy the same atomic site of Wyckoff position 1a. Electrical resistivity and magnetic susceptibility show the superconducting transition at 22.5 K. The transition temperature (T_c) of (La,Na,K)Fe₂As₂ is comparable with that of 122-type (La,Na)Fe₂As₂ and 1144-type (La,Na)AFe₄As₄ (A = Rb, Cs), while being more than 10 K lower than those of typical 122- and 1144-type FeSCs. The results suggest that the random distribution of La³⁺ and Na⁺ ions is the main reason for lower T_c in the AE = (La,Na) 122-type and 1144-type FeSCs.

SUBMITTER: Kawashima K

PROVIDER: S-EPMC6235837 | biostudies-literature | 2018 Nov

REPOSITORIES: biostudies-literature

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Superconductivity in a 122-type Fe-based compound (La,Na,K)Fe2As2.

Kawashima Kenji K Ishida Shigeyuki S Fujihisa Hiroshi H Gotoh Yoshito Y Yoshida Yoshiyuki Y Eisaki Hiroshi H Ogino Hiraku H Iyo Akira A

Scientific reports 20181114 1

We synthesized a Fe-based superconductor (FeSC), (La,Na,K)Fe2As2, and characterized its superconducting properties. It was found that (La,Na,K)Fe2As2 has a 122-type (ThCr2Si2-type) structure with a space group I4/mmm (No. 139), identical to (Ba,K)Fe2As2 and (La,Na)Fe2As2 but distinct from so-called 1144-type FeSCs such as CaKFe4As4 and (La,Na)CsFe4As ...[more]

PMID: 30429484

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Project description:We synthesized and characterized a novel iron(II) aceto EMIM coordination compound, which has a simplified empirical formula Fe4(OAc)10[EMIM]2, in two different hydration forms: as anhydrous monoclinic compound and triclinic dihydrate Fe4(OAc)10[EMIM]2·2H2O. The dihydrate compound is isostructural with recently reported Mn4(OAc)10[EMIM]2·2H2O, while the anhydrate is a superstructure of the Mn counterpart, suggesting the existence of solid solutions. Both new Fe compounds contain chains of Fe2+ octahedrally coordinated exclusively by acetate groups. The EMIM moieties do not interact directly with the Fe2+ and contribute to the structural framework of the compound through van der Waals forces and C-H···O hydrogen bonds with the acetate anions. The compounds have a melting temperature of ∼94 °C; therefore, they can be considered metal-containing ionic liquids. Differential thermal analysis indicates three endothermic transitions associated with melting, structural rearrangement in the molten state at about 157 °C, and finally, thermal decomposition of the Fe4(OAc)10[EMIM]2. Thermogravimetric analyses indicate an ∼72 wt % mass loss during the decomposition at 280-325 °C. The Fe4(OAc)10[EMIM]2 compounds have higher thermal stability than their Mn counterparts and [EMIM][OAc] but lower compared to iron(II) acetate. Temperature-programmed desorption coupled with mass spectrometry shows that the decomposition pathway of the Fe4(OAc)10[EMIM]2 involves four distinct regimes with peak temperatures at 88, 200, 267, and 345 °C. The main species observed in the decomposition of the compound are CH3, H2O, N2, CO, OC-CH3, OH-CO, H3C-CO-CH3, and H3C-O-CO-CH3. Variable-temperature infrared vibrational spectroscopy indicates that the phase transition at 160-180 °C is associated with a reorientation of the acetate ions, which may lead to a lower interaction with the [EMIM]+ before the decomposition of the Fe4(OAc)10[EMIM]2 upon further heating. The Fe4(OAc)10[EMIM]2 compounds are porous, plausibly capable of accommodating other types of molecules.

Dataset Information

Superconductivity in a 122-type Fe-based compound (La,Na,K)Fe₂As₂.

Publications

Superconductivity in a 122-type Fe-based compound (La,Na,K)Fe<sub>2</sub>As<sub>2</sub>.

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