A(NH3)xFePS3 (A = Li, K): intercalated Fe thiophosphate via the liquid ammonia method

Abstract

Metal phosphorus trichalcogenides (MPX₃) are of great interest since these layered materials exhibit wide applications in optical, electrical and magnetic fields. An effective chemical intercalation route for MPX₃ which could regulate their physical properties, however, is still lacking. In this work, we show that the liquid ammonia method is an efficient route to co-intercalate alkali metals and NH₃ molecules into the gaps in FePS₃. After intercalation, the interlayer distance is significantly enlarged by ∼3 Å while the monoclinic lattice (C2/m space group) is still maintained. The structure refinement and EDS measurement suggest that intercalation does not induce any Fe vacancy, thus leading to electron transfer from the alkali metal to [FePS₃] layers. Interestingly, magnetic susceptibility shows that the intrinsic anti-ferromagnetic transition in the FePS₃ matrix is completely suppressed by this intercalation, whereas a spin-glass state is observed in A(NH₃)_xFePS₃ (A = Li, K) in the lower temperature range (<50 K). The intercalation described in this work is reversible: the alkali metal can be easily de-intercalated using a two-step route and the anti-ferromagnetism reappears accordingly. Meanwhile, the liquid ammonia method is also shown to be efficient at intercalating other MPS₃ materials (M = Mn, Co, Ni). Our work not only enriches the intercalation chemistry in the MPX₃ system but also provides an excellent route to regulate the magnetic properties of these layered materials.