Microstructural properties of K _0.8 Fe _1.6 S ₂ , K _0.8 Fe _1.75 Se _2-y S _y (0 ≤ y ≤ 2) and K _0.8 Fe

Abstract

The structural features of the antiferromagnetic K0.8Fe1.6S2 have been studied in the temperature range from 300 K up to 700 K by means of in situ transmission electron microscopy (TEM). The superstructure with a wave vector originating from a Fe-vacancy order has been clearly observed; moreover, the structural analysis shows that K0.8Fe1.6S2 undergoes a transition from the Fe-vacancy order to disorder at about 585 K. The S substitution effect on the phase separation and superconductivity in the K0.8Fe1.75Se2−ySy materials has been systematically investigated by SEM and TEM structural analyses, as well as by electrical resistivity measurements. Our experimental results reveal that the S element adopts a homogeneous distribution in all investigated materials, and the essential phase-separation nature is very similar to what was observed in the K0.8Fe1.75Se2 superconductor. A phase-separated state formed by the coexistence of two Fe-vacancy orders with wave vectors and in K0.8Fe1.5+xS2 (0 < x < 0.1) has been briefly discussed.

Two spatially separated phases in semiconductingRb0.8Fe1.5S2

“…2(a) on a logarithm scale represents clear semiconducting behavior. This semiconducting characteristic is quite similar to that of the potassium compound with equivalent composition, K 0.8 Fe 1.5 S 2 [40]. These results reveal, as expected, that Rb 0.8 Fe y S 2 and K 0.8 Fe y S 2 have similar transport characteristics.…”

“…Therefore, determining the origin of the in-plane AF order in the semiconducting phase and its relationship with superconductivity is crucial to understanding the mechanism of superconductivity in the A x Fe y Se 2 system. The low-temperature electrical resistivity of the 245 system can be changed from insulating to semiconducting or superconducting by controlling the iron content as in A 0.8 Fe y Se 2 , generally in concert with the alkali concentration A, or by substitution of sulfur on the selenium sites as in A 0.8 Fe y Se 2−z S z [32,[36][37][38][39][40]. In studies to date, changing the iron content of the pure Se two-phase material results in the sudden disappearance of the superconductivity, while sulfur substitution for selenium appears to suppress superconductivity gradually, resulting in a semiconducting ground state [39].…”

Two New MOFs Based on Cu2 Paddlewheel Units and Biphenyltetracarboxylate Ligands with a Different Degree of Fluorination

“…[7,10,[17][18][19] In CuMBTC and CuEBTC, methyl and ethyl groups, respectively, were introduced in ortho position to the carboxylate groups of a trimesate ligand. [22] For these MOFs also comparable large torsion angles were reported ( Table 2). As strong electronic effects can be excluded for methyl and ethyl groups, one can conclude that these torsion angles are mostly affected by steric effects, i.e.…”

Hydrophobic Metal–Organic Frameworks: Assessment, Construction, and Diverse Applications

“…MOFs synthesized from some tritopic, tetratopic, and octatopic carboxylic acid ligands have also shown characteristics of hydrophobicity. [121][122][123][125][126][127][128] Cai et al reported two Cu 2 paddlewheel SBU based MOFs, [Cu 3 (mbtc) 2 ] (CuMBTC) and [Cu 3 (ebtc) 2 ] (CuEBTC), which were obtained from methyl-and ethyl-groupfunctionalized H 3 btc ligands, H 3 mbtc and H 3 ebtc, respectively. [121] The assembly of H 3 btc and Cu 2 paddle-wheel SBUs produces the well-studied MOF [Cu 3 (btc) 2 ] (HKUST-1, also called CuBTC or MOF-199).…”