Germanium-rich GeSbTe alloys have recently emerged as promising materials for embedded phase change memories of interest for applications in the automotive sector thanks to the high crystallization temperature of their amorphous phase. Crystallization of Ge-rich GeSbTe alloys can lead to phase separation with segregation of crystalline Ge. The inhomogeneity of the resulting system brings, however, some drawbacks such as the drift of the electrical resistance with time of the crystalline phase. To mitigate these effects, a better understanding of the decomposition process is needed. In this work, we performed density functional calculations on possible decomposition pathways of the alloy as an example of Ge-rich GeSbTe alloy on the Ge- pseudobinary line. The energetics of the transformation into crystalline Ge and a less Ge-rich alloy is investigated as well as the structural, electronic, and vibrational properties of some possible decomposition products such as or , among several others, in both the crystalline and amorphous phases.