Structural investigation of the ammonium intercalates of titanium and niobium disulfides

The ammonium intercalates (NH⁺₄)_y'TiS^y'-₂, y'=0.21 and 0.23, and (NH⁺₄)_0.19NbS^0.19- ₂ have been synthesized and characterized by X-ray powder diffraction, thermogravimetric analysis, vapor pressure measurements and evolved gas analysis. These compounds have six-layer stage-II structures with rhombohedral, or nearly rhombohedral, symmetry. A comparison of calculated and observed X-ray powder diffraction intensities for (NH⁺₄)_0.21TiS^0.21-₂ (a=3.1416 and c=42.73 A ̊) shows good agreement with trigonal prismatic NH⁺₄ coordination in the van der Waals gap. X-ray powder diffraction also suggests the presence of substantial local-layer disorder for many of these compounds, which is probably associated with the low temperatures required for synthesis.