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

Abstract

The progress of materials discovery of iron-based superconductors is reviewed with the emphasis on the valence states and chemical bonds of arsenic. We demonstrate that monovalent As -produces the 112-type CaFeAs 2 with arsenic zigzag chains. When co-doping of La and Sb is performed, the superconducting transition temperature rises to 47 K. In the 10-4-8-type Ca 10 (Pt 4 As 8 )(Fe 2−x Pt x As 2 ) 5 , the divalent As 2-produces As 2 molecules, and creates an interlayer substance with PtAs 4 planar squares. The maximum superconducting transition temperature is 38 K. In the 122-type CaFe 2 As 2 , Rh doping induces a lattice collapse transition accompanying the formation of As 2 molecules between the adjacent FeAs layers. This transition can be viewed as a valence transition between As 3-and As 2-. These properties of arsenic that produces various chemical bonds can be used to create new superconducting materials.

Structural and magnetic studies on SrCo₂As₂ and Ca(Co_1-xFe_x)_yAs₂ compounds using x-ray and neutron scattering

“…As shown in Fig. 7.1 Ni is substituted by Cu [85,32]. Such work may lead to finding more insight about the collapsed tetragonal phase.…”

“…The emergence of the cT phase in CaM 2 As 2 is proposed to occur somewhere in between M = Fe and Co as shown in Fig. 2.7 [85,32].…”

“…1.1 and the reasons for choosing the particular directions can be well described by using the Fig. 2.7 [15,32]. already well understood and does not show the cT phase for x ≥ 0.91 [33,34,35].…”

Wave functions, electronic localization, and bonding properties for correlated materials beyond the Kohn-Sham formalism

“…As well as superconductivity, CaFe 2 As 2 has displayed the shapememory alloy and superelasticity effects [51]. Chemical substitution enables the fine-tuning of CaFe 2 As 2 properties [52][53][54][55][56][57][58].…”

Temperature-dependent local structure and superconductivity of BaPd2As2 and SrPd2As2

“…Iron-based superconductors are a good example in which interplay between structural transition and superconductivity exists and the structural parameters have direct interplay with spin, charge, and orbital fluctuations, important for the superconductivity [3]. Incidentally, such an intriguing interplay is strictly related to the As chemistry, therefore interaction between arsenic 4p and iron 3d electrons and bonding of As atoms [4]. The so-called "122" compounds [5,6] forming a body-centered tetragonal ThCr 2 Si 2 -type structure (space group I 4/mmm) at room temperature have been main systems to study these correlations [7,8].…”