Template-induced structural phase transition of GeS2 and GeSe2 in organic–inorganic hybrid mesostructures

We have synthesised layered organic–inorganic hybrid mesostructures of GeX2 (X=S, Se) and corresponding bulk inorganic reference samples using various precursors and different growth temperatures. X-ray as well as TEM studies confirm the high degree of order of the superstructure of the synthesised organic–inorganic hybrids. The samples were studied by Raman spectroscopy to obtain information on their microscopic structure. With increasing growth temperature, the bulk GeS2 reference samples exhibit an abrupt structural phase transition from the amorphous to the α-crystalline phase. In contrast, the GeS2 layers of the hybrid mesostructures transform rather continuously with increasing growth temperature from the amorphous network to a quasi-crystalline Ge4X6+4/2 network consisting of Ge4X104− adamantan units, i.e. the organic template induces constraints which lead to a structural phase diagram of the nanostructured GeS2 other than for bulk GeS2. By rescaling the Raman spectra of the new quasi-crystalline Ge4S6+4/2 and Ge4Se6+4/2 phases with the appropriate scaling factors for bond-bending and bond-stretching modes derived from the α- and β-crystalline GeX2 phases, it can be shown that both Ge4X6+4/2 layers have the same microscopic structure.