G e 2 S b 2 T e 5 polycrystalline films either in the trigonal stable phase or in the metastable rock-salt structure have been irradiated with 150 keV Ar+ ions. The effects of disorder are studied by electrical, optical, and structural measurements and density functional theory (DFT) simulations. In the metastable structure, the main effect of ion irradiation is a progressive amorphization, with an optical threshold at a fluence of 3× 10 13 c m− 2. For the trigonal structure, a metal-insulator transition and a crystalline transition to rock-salt structure occur prior to amorphization, which requires a fluence of 8× 10 13 c m− 2. The bonds of Te atoms close to the van der Waals gaps, present in the trigonal phase and identified by Raman spectroscopy, change as a function of the disorder induced by the irradiation. Comparison with DFT simulations shows that ion irradiation leads to the gradual filling of the van der Waals gaps with …