Iron arsenide superconductors (CaFeAs)₁₀M_nAs₈ with metallic interlayers (M = Pt, Pd; n = 3, 4)

Abstract

The compounds referred to as 1038 and 1048 phases (CaFeAs)10PtnAs8 (n = 3,4) are the structurally most complex iron arsenide superconductors and the first examples with metallic interlayers. The electronic subsystems of FeAs and PtnAs8 layers hardly interact and the contribution of the metallic PtnAs8 interlayers to the Fermi surface is so small that the typical nesting is not degraded. (CaFeAs)10Pt3As8 is the parent compound of the 1038/1048 materials which undergoes the typical magneto‐structural phase transition in spite of the already triclinic lattice. Superconductivity is controlled by the same doping mechanisms as known from simpler FeAs systems. High critical temperatures up to 38 K occur in both 1038 and 1048 phases if the FeAs layers are clean (free from Pt) and electron doped by charge transfer either from Pt4As8 in 1048 or by rare‐earth doping of the calcium layer in 1038 compounds. The presence of two negatively charged layers (FeAs)δ− and (PtnAs8)δ− which compete for the electrons transferred from the Ca2+ ions is unique in the family of iron arsenide superconductors. Geometric incompatibilities of the FeAs and PtnAs8 slabs cause severe stacking disorder. The robustness of superconductivity against low lattice symmetry and significant structural imperfection of the interlayer is quite remarkable and underlines that the FeAs slabs are the key in controlling and understanding high‐temperature superconductivity in iron arsenides. Crystal structure of (CaFeAs)10Pt3As8 and the Pt3As8 layer.

A soft molecular 2Fe–2As precursor approach to the synthesis of nanostructured FeAs for efficient electrocatalytic water oxidation

“…Among TM arsenides, iron arsenide (FeAs) based materials have attracted much attention and have been studied extensively for their unconventional superconductivity. [33][34][35][36][37] Similarly, FeAs has recently been utilized as a promising anode for Li-ion batteries, 38 however, its potential application in electrocatalytic water-splitting is currently unexplored due to concerns about toxicity and possible derived contamination. However, pros for the investigation of TM arsenides as OER electro(pre)catalysts have recently been noted in the literature.…”

Arsenic chemistry of iron-based superconductors and strategy for novel superconducting materials

“…Therefore, when the Fe favoring tetrahedral coordination is mixed with Pt favoring planar square coordination, it appears that, because they do not favor formation of a solid solution in nature, a new compound, 10-4-8-type, is produced. In the same way, compounds including the PdAs 4 planar squares [34][35][36] and IrAs 4 planar squares [37][38][39][40] were discovered. Since Ir 2+ favors tetrahedral coordination rather than planar square coordination, the crystal structure is unstable, and shows a structural phase transition at low temperatures [38,39].…”

Optical Properties in The Hole-Doped Ca8.5Na1.5(Pt3As8)(Fe2As2)5 Single Crystal

“…The Ca10-3-8 parent compound, unlike other typical FeAs superconductors, is semiconducting and antiferromagnetically ordered without any further reduction in crystal symmetry at T N ~ 110 K. The doping effect in the parent compound leads to superconductivity 8 . Electron doping effect occurs when La is replaced at Ca site and Pt is substituted at Fe site, and hole doping effect can occur when Na is substituted at Ca site.…”