Superconductivity in solid-state synthesized (Li,Fe)OHFeSe by tuning Fe vacancies in FeSe layer

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

“…The precursors spontaneously self-assemble into alternating quasi-atomic Cu-Fe-S sulfide and Mg hydroxide sheets in the hydrothermal process through a mechanism that still needs to be understood. The structure of valleriites formed by incommensurate 2D layers allows to vary widely, and to some extent independently, their composition and then properties, including replacement both of metals and chalcogenide atoms [30][31][32][33][34][42][43][44][45][46][47][48][49][50]. On the other hand, the counterparts affect each other via the electric charges and probably other factors; this makes possible to finely adjust the material characteristics.…”

“…The more positive charge of sulfide layers leads, among other effects, to a reduced density of minority spins and an enhanced number of unpaired spins at Fe 3+ sites, creating the large local hyperfine fields and peculiar magnetic properties of valleriite. The charges can be adjusted and probably reversed by incorporating, for example, monovalent cations akin to Li + ; this would allow to modify also the electronic and optical properties, including possible superconductivity [46][47][48][49][50][51].…”

“…Attempts to synthesize valleriite via thermal sintering or hydrothermal route have been undertaken [30,[35][36][37]41,42] but produced mixtures of valleriite (less than 50%) with chalcopyrite, magnetite and other by-products. In recent years, a number of similar composites with the layered structure constructed by iron selenide and lithium-based hydroxides (Li1-xFex)(OH)FeSe [43][44][45][46][47] have been prepared and studied as superconductors with the critical temperature Tc up to 40 K. Such materials as [(Fe,Al)(OH)2][FeSe]1.2 [48],…”

Superconductivity at 40 K in Lithiation-Processed [(Fe,Al)(OH)2][FeSe]1.2 with a Layered Structure

“…Thus, the lithiated sample displays the decrease of Fe content in the (Fe,Al)(OH)2 layer and the increase of Fe content in the FeSe layer with the ratio of Fe : Se to be 1 : 1, just like the case of the lithiated (Li,Fe)OHFeSe. 12,24 In addition, the ion radii of Li + is about 0.59 Å 25 , the change of c-axis lattice parameters before and after lithiation is less than 0.3 Å, so intercalation of Li + between two layers may not occur just like the situation of the lithiation of (Li,Fe)OHFeSe. 12,13 More 4) Å, which are also in accordance with the XRD refinement of the lithiated sample, respectively.…”

“…Such insulating behavior is similar to that of K2Fe4Se5 and solid-state synthesized (Li,Fe)OHFeSe, which is attributed to the large amount of Fe vacancies in the FeSe layer. 24,27 Figure 3b shows the temperature dependent magnetic susceptibility of the as-synthesized sample. As shown in Figure 3b, a Curie-Weiss paramagnetism-like behavior is observed.…”