Tochilinite and Selenotochilinite: Heterostructures of Layered Double Hydroxides with Layered Tetragonal FeS and FeSe

The design of heterostructures provides a promising avenue for discovering and manipulating emergent quantum phenomena within correlated electron systems. This approach is particularly relevant for iron-based chalcogenides, such as superconducting FeSe, whose properties can be tuned with different intercalates. We report the hydrothermal synthesis of a family of layered double hydroxide (LDH) intercalated iron chalcogenides, [Mg_1-<i>x</i>Al_<i>x</i>(OH)₂]Fe_1-<i>y</i>S and [M_1-<i>x</i>Al_<i>x</i>(OD)₂]Fe_1-<i>y</i>Se (M = Mg, Mn, Fe), with <i>x</i>, <i>y</i> < 0.33. We introduce the Mn-containing selenide as a new member, synthesized hydrothermally, broadening the accessible compositional range. We previously reported some details of the synthesis of the Mg- and Fe-based analogues; here, we provide new structural insights obtained through combined selected-area electron diffraction, neutron and X-ray powder diffraction, and pair distribution function analysis. Selected-area electron diffraction of the sulfide analogue reveals a strongly modulated supercell with 2-fold symmetry, consistent with the mineral tochilinite. In contrast, the selenide analogue largely preserves tetragonal symmetry with weak superlattice reflections from subtle periodic modulation or ordering. Guided by electron diffraction, neutron scattering, and PDF analysis, we construct and validate a new FeSe-LDH heterolayer model that retains 4-fold symmetry. This study strengthens the current structural understanding of these lesser-known intercalated iron chalcogenide misfit heterostructures.