The structures of two intercalation compounds, Ge similar to 0.2NbSe2 and Ge similar to 0.3NbS2 were investigated by single crystal X-ray diffraction and electron microscopy (selected area electron diffraction (SAED), high resolution electron microscopy (HRTEM) and X-ray microanalysis by energy dispersive spectroscopy (XEDS)). Crystal structure determinations of the average structure of the intercalation compounds 2H-Ge0.217NbSe2 and 4H-Ge0.288NbS2 are reported: the selenide compound crystallizes in the space group P6(3)/mmc with a = 3.4560(9) angstrom and c = 12.966(3) angstrom and adopts the 2H-NbSe2 structure-type, while the sulfide compound crystallizes in the P6(3)mc Space group, with a = 3.3392(9) angstrom and c = 25.404(7) angstrom with a structure-type 4H(c)-NbS2 which it is known for TaSe2. In both structures the germanium atoms are located in the empty octahedral positions of the van der Waals gap between the NbX2 (X = S, Se) layers. Electron diffraction patterns from several GexNbSe2 crystal flakes show different superstructures and exhibit diffracted diffuse intensity: weak satellites corresponding to a(0)root 3 x a(0)root 3 and 2a(0) x 2a(0) superstructures were observed for x similar to 0.15 (a(0) is the basal lattice parameter of the host structure). For x similar to 0.25-0.33, the same type of satellite is observed with a stronger intensity. For x similar to 0.5 only satellites corresponding to the a(0)root 3 x a(0)root 3 superstructure were present. In the case of GexNbS2, with 0.10 < x < 0.25, the germanium atoms are ordered in domains with an a(0)root 3 x a(0)root 3 superstructure. In some crystals disorder along the c-axis has been observed. (C) 2009 Elsevier Ltd. All rights reserved.