Heterolayered materials can made by stacking monolayers of different 2D materials could exhibit properties inherited from either of the parent materials or both. Symbiotic relationship between the layers could lead to superior properties than constituent components or to new emergent properties that are not present in the individual bulk compounds makes these compounds interesting. For our work, we chose tetragonal iron selenide with anti-PbO structure type as the host material. It exhibits superconducting transition at 8 K and can be increased up to 46 K through structural modifications via intercalation. Vacant iron sites in Fe1-xSe lead to a partial negative charge on the layer. These FeSe layers are intercalated by hexagonal layered double hydroxides, LDH, made up of positively charged layers with anionic guest molecules occupying the interlayer space. Intrinsic opposite partial charges and lamellar structure with weak van der Waals forces holding the layers together in both these materials makes it possible for in-situ growth of FeSe-LDH heterostructures. We have synthesized polycrystalline powders of M2+2/3M3+1/3(OH)2FeSe with Mg, Mn, Fe as divalent and Al as trivalent cation. Because of the mismatch between intralayer tetragonal and hexagonal symmetries, the product heterostuctures are incommensurate. Precise crystal structure determination is necessary to explain the emergent properties, and since the synthesis attempts yielded polycrystalline powders in all cases, we aim to obtain a structure solution from powder diffraction data. We pair the synchrotron X-ray with neutron data to help locate lighter elements such as hydrogen atoms in the structure, because of their drastic difference in neutron scatter cross-section as compared to X-rays. However, we found broad diffraction peaks and diffuse scattering masking structural information probably due to small crystallite sizes and absence of long-range periodicity. Along with the Bragg peak analysis, we use pair distribution function (PDF) analysis which is very helpful when determining structure of materials with short range order, since the technique does not rely on periodicity. These results would help devise strategies to synthesize and understand structures of hybrid materials using LDH and TMCh, opening up access to a class of functional materials with interesting properties.

Two-dimensional Iron selenide heterolayer superlattices

ACS Spring 2022

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