Iron-based superconductors have been a hot area for their unconventional superconductivity since their discovery in 2006. Besides its superconductivity, FeSe, with a critical temperature (Tc) of 8 K, can be an ideal host for intercalation chemistry because of its layered nature and ability to accept charged and neutral species as intercalates. FeSe assumes the so-called anti-PbO type structure, where FeSe4 tetrahedra edge-share to form 2D sheets held by weak van der Waals interactions. Its Tc can be increased to 42-44 K by inserting cations or neutral species. Recently, we have found that alkali metal hydroxide intercalations into anti-PbO type FeS could also improve its Tc. Therefore, by intercalating new layers into these 2D materials, new properties may emerge. To look beyond iron chalcogenides (FeCh, Ch = Se, S), our group has recently prepared the anti-PbO type CoCh and applied similar intercalation chemistry of FeCh. The 2D tetragonal CoCh are prepared through de-intercalation of the ThCr2Si2-type KCo2Ch2 precursor. Intercalation of lithium ethylenediamine into the CoSe layers has been successful and has expanded the layer spacing from 5.33 Å to about 11 Å. Because of its low thermal stability and smaller layer spacing compared to FeSe (5.52 Å), it is very difficult to intercalate LiOH. At elevated temperature, CoSe forms the cobalt seleno-pentlandite before the insertion of LiOH layer could occur. Therefore, we tried to stabilize CoSe by doping Fe into the Co sub-lattice and with only a few percent of Fe, new LiOH intercalated mixed phases were synthesized. Moreover, we have successfully prepared a complete series of solid-solutions of LiOHCo1-xFexSe by varying x (0 – 1). We have been able to obtain a phase diagram of this mixed phase along with their electrical resistivity, magnetic susceptibility, X-ray diffraction, neutron scattering, and elemental analysis.

Intercalation chemistry of CoSe and Co1-xFexSe mixed phase

253rd National Meeting (2017)

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