Si-Qi Wu

Anomalous Eu Valence State and Superconductivity in Undoped Eu3Bi2S4F4

We have synthesized a novel europium bismuth sulfofluoride, Eu3Bi2S4F4, by solid-state reactions in sealed evacuated quartz ampules. The compound crystallizes in a tetragonal lattice (space group I4/mmm, a = 4.0771(1) Å, c = 32.4330(6) Å, and Z = 2), in which CaF2-type Eu3F4 layers and NaCl-like BiS2 bilayers stack alternately along the crystallographic c axis. There are two crystallographically distinct Eu sites, Eu(1) and Eu(2) at the Wyckoff positions 4e and 2a, respectively. Our bond valence sum calculation, based on the refined structural data, indicates that Eu(1) is essentially divalent, while Eu(2) has an average valence of ∼ +2.64(5). This anomalous Eu valence state is further confirmed and supported, respectively, by Mössbauer and magnetization measurements. The Eu(3+) components donate electrons into the conduction bands that are mainly composed of Bi 6px and 6py states. Consequently, the material itself shows metallic conduction and superconducts at 1.5 K without extrinsic chemical doping.

Superconductivity in KCa2Fe4As4F2 with Separate Double Fe2As2 Layers

We report the synthesis, crystal structure, and physical properties of a quinary iron arsenide fluoride, KCa2Fe4As4F2. The new compound crystallizes in a body-centered tetragonal lattice (space group I4/mmm, a = 3.8684(2) Å, c = 31.007(1) Å, Z = 2) that contains double Fe2As2 conducting layers separated by insulating Ca2F2 layers. Our measurements of electrical resistivity, direct-current magnetic susceptibility, and heat capacity demonstrate bulk superconductivity at 33 K in KCa2Fe4As4F2.

Crystal structure and superconductivity at about 30 K in ACa2Fe4As4F2 (A = Rb, Cs)

We have synthesized two iron fluo-arsenides ACa2Fe4As4F2 with A = Rb and Cs, analogous to the newly discovered superconductor KCa2Fe4As4F2. The quinary inorganic compounds crystallize in a body-centered tetragonal lattice with space group I4/mmm, which contain double Fe2As2 layers that are separated by insulating Ca2F2 layers. The electrical and magnetic measurements on the polycrystalline samples demonstrate that the new materials undergo superconducting transitions at Tc = 30.5 and 28.2 K, respectively, without extrinsic doping. The correlations between Tc and structural parameters are discussed.摘要本文合成了与新发现的KCa2Fe4As4F2超导体结构相同的两种铁砷氟化物ACa2Fe4As4F2 (A = Rb, Cs). 该五元无机物具有四方体心晶格,空间群为I4/mmm, 包含被Ca2F2绝缘层分开的双Fe2As2层. 对多晶样品的电阻和直流磁化率的测量表明, ACa2Fe4As4F2 (A = Rb, Cs)样品无需外在掺杂即呈现出30.5和28.2 K的超导电性. 文中还讨论了其Tc与晶体结构参数间的关联.

Synthesis, Crystal Structure and Superconductivity in RbLn2Fe4As4O2 (Ln = Sm, Tb, Dy, and Ho)

We have synthesized four iron-based oxyarsenide superconductors RbLn2Fe4As4O2 (Ln = Sm, Tb, Dy and Ho) resulting from the intergrowth of RbFe2As2 and LnFeAsO. It is found that the lattice match between RbFe2As2 and LnFeAsO is crucial for the phase formation. The structural intergrowth leads to double asymmetric Fe2As2 layers that are separated by insulating Ln2O2 slabs. Consequently, the materials are intrinsically doped at a level of 0.25 holes/Fe-atom, and bulk superconductivity emerges at Tc = 35.8, 34.7, 34.3, and 33.8 K, respectively, for Ln = Sm, Tb, Dy, and Ho. Investigation of the correlation between crystal structure and Tc suggests that interlayer couplings may play an additional role for optimization of superconductivity.

Superconductivity at 35 K by self doping in RbGd2Fe4As4O2

We report synthesis, crystal structure and physical properties of a novel quinary compound RbGd2Fe4As4O2. The new iron oxyarsenide is isostructural to the fluo-arsenide KCa2Fe4As4F2, both of which contain separate double Fe2As2 layers that are self hole-doped in the stoichiometric composition. Bulk superconductivity at [Formula: see text] K is demonstrated by the measurements of electrical resistivity, dc magnetic susceptibility and heat capacity. An exceptionally high value of the initial slope of the upper critical field ([Formula: see text]d[Formula: see text]/d[Formula: see text] [Formula: see text] T K-1) is measured for the polycrystalline sample.

Superconductivity at 33–37 K in ALn2Fe4As4O2(A=Kand Cs;Ln=lanthanides)

We have synthesized 10 new iron oxyarsenides, K

Cu{001}c(2 x 2)-Pd: An ordered surface alloy.

Ln_2

Epitaxial growth of body-centered-tetragonal copper.

Fe

Structural and electronic properties of a surface alloy of Pd and Cu on Cu{001}

_4

Structural reactions of Si{111} with cobalt and formation of cobalt disilicide

As