Microscopic evidences for intercalation of nickel and iron into layered oxysulfide La2O2S2

Abstract

2D transition metal chalcogenides have been examined as versatile platforms for exotic quantum phenomena, optoelectronic and photocatalytic applications. La2O2S2, a layered oxysulfide built of [La2O2]2+ slabs and 2D arrays of [S2]2- dimers, was recently found to be a promising precursor to fabricate such 2D materials. Redox reactions with external zerovalent metals cleaved its S–S bonds, triggering intercalation of those metal guests. This process serves as a novel approach to construct 2D metal sulfides between rigid [La2O2]2+ slabs, but so far demonstrated only for Cu + cations. We herein report that the same intercalation process takes place also when Ni and Fe were used as reagents. While XRD indicated that the reactions with Ni and Fe converted La2O2S2 into the sulfur-deficient La2O2S1.5-x (0 ≤ x ≤ 0.38) phase, our TEM analyses evidenced diffusion of those metals in between [La2O2]2+ slabs at the local scale. This finding suggested the formation of 2D nickel and iron sulfides intergrown with [La2O2]2+ slabs, either as the unprecedented La–O-M-S (M = Ni, Fe) phase, or a biphasic heterostructure. In addition, our computational structure prediction also supported stability of such intergrowth [La2O2][MxS2-y] structures, encouraging future attempts to isolate those elusive 2D materials.