Ge1-xSnx alloys with x concentration up to 0.14 were grown on Ge(001) and GaAs(001) substrates in a conventional R. F. Magnetron Sputtering system at low substrate temperatures. The structural characteristics of these alloys were studied for different Sn concentrations between 1 to 14 % by high resolution X ray diffraction, and Raman spectroscopy. Contrasting characteristics of the grown layers are observed if the Sn concentration is larger or smaller than 6 % as revealed by X-ray diffraction and Raman spectroscopy.