Superconductivity at 40 K in Lithiation-Processed [(Fe,Al)(OH)₂][FeSe]_1.2 with a Layered Structure

Abstract

Exploration of new superconductors has always been one of the research directions in condensed matter physics. We report here a new layered heterostructure of [(Fe,Al)(OH)2][FeSe]1.2, which is synthesized by the hydrothermal ion-exchange technique. The structure is suggested by a combination of X-ray powder diffraction and the electron diffraction (ED).[(Fe,Al)(OH)2][FeSe]1.2 is composed of the alternating stacking of tetragonal FeSe layer and hexagonal (Fe,Al)(OH)2 layer. In [(Fe,Al)(OH)2][FeSe]1.2, there exists mismatch between the FeSe sub-layer and (Fe,Al)(OH)2 sub-layer, and the lattice of the layered heterostructure is quasi-commensurate. The as-synthesized [(Fe,Al)(OH)2][FeSe]1.2 is non-superconducting due to the Fe vacancies in the FeSe layer. The superconductivity with a Tc of 40 K can be achieved after a lithiation process, which is due to the elimination of the Fe vacancies in the FeSe layer. The Tc is nearly the same as that of (Li,Fe)OHFeSe although the structure of [(Fe,Al)(OH)2][FeSe]1.2 is quite different from that of (Li,Fe)OHFeSe. The new layered heterostructure of [(Fe,Al)(OH)2][FeSe]1.2 contains an iron selenium tetragonal lattice interleaved with a hexagonal metal hydroxide lattice. These results indicate that the superconductivity is very robust for FeSe-based superconductors. It opens a path for exploring superconductivity in iron-base superconductors.

Synthesis and characterization of nanoscale composite particles formed by 2D layers of Cu–Fe sulfide and Mg-based hydroxide

“…Attempts to synthesize valleriite via thermal sintering or a hydrothermal route have been undertaken 33,38–40,44,45 but they produced mixtures of valleriite (less than 50%) with chalcopyrite, magnetite and other by-products. In recent years, a number of similar composites with a layered structure constructed by iron selenide and lithium-based hydroxides (Li 1− x Fe x )(OH)·FeSe 46–50 have been prepared and studied as superconductors with the critical temperature T c up to 40 K. Materials such as [(Fe,Al)(OH) 2 ][FeSe] 1.2 , 51 [(Li 0.8 Fe 0.2 )OH]Fe(S 1− x Se x ), 52 (Na x Fe 1— x )(OH)FeS 53 and intercalated iron chalcogenides 54 were also obtained in efforts, though unsuccessful yet, to enhance the T c .…”

Synthesis and characterization of nanoscale composite particles formed by 2D layers of Cu-Fe sulfide and Mg-based hydroxide

“…The flake-like nanoparticles composed of altering quasi-atomic Cu-Fe-S sulfide and Mg hydroxide sheets are manufactured in the environment-friendly hydrothermal process using common reagents. Such a chalcogenide-hydroxide incommensurate structures looks unusual and complex but there exist a number of natural [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] and synthetic [43][44][45][46][47][48][49][50][51] layered materials, suggesting that those are quite stable and spontaneously assemble via a mechanism that needs to be understood. The composition and then morphology and properties of the materials can be engineered by varying the nature and concentrations of precursors, modifiers, dopants far beyond those used in this case study.…”

“…It is worth recalling, for example, that similar composite of metal (Li and others) hydroxide and iron selenide monolayers are superconductors. [43][44][45][46][47][48][49][50][51] The large surface area, layered structure, and specific surface properties are essential for applications of the nanoscale valleriites as adsorbents, catalysts, sensors, electrode materials, etc. The feasible peptization of the materials paves the way for their utilization as quantum dots and inks or manufacturing thin films on various supports.…”

“…The attempts to synthesize valleriite via thermal sintering or hydrothermal routes have been undertaken [30,[35][36][37]41,42] but mixtures of valleriite with chalcopyrite, magnetite and other byproducts have been obtained. It should be noted that a number of layered composites of lithiumbased and some other hydroxides and iron selenides (Li1-xFex)(OH)FeSe, [43][44][45][46][47] [(Fe,Al)(OH)2][FeSe]1.2, [48] iron sulfides [(Li0.8Fe0.2)OH]Fe(S1-xSex), [49] (NaxFe1-x)(OH)FeS [50] and similar [51] have been prepared and studied with focus on their superconductivity (critical temperature Tc up to 40 K). However, the compounds with alkaline metal hydroxides tend to hydrolysis hindering their exploration and wider exploitation.…”

A novel iron-based superconductor synthesized by the ion exchange technique

“…However, controlling Fe vacancies in the FeSe plane is complicated and time-consuming. For example, (Li,Fe)OHFeSe [19] and [(Fe,Al)(OH) 2 ][FeSe] 1.2 [20] crystals are usually synthesized by ion exchange technique using insulating K 0.8 Fe 1.6 Se 2 single crystal as the matrix. In order to make up for the Fe vacancies in the FeSe layer, we must add a large amount of nano-iron powder as the iron source to the reaction system or use post-processing methods.…”