Metastable cubic Ge2Sb2+x
Te5 compounds, which can be prepared only as thin films, have been studied by both of neutron and x-ray powder diffraction measurements. Large displacement of germanium atoms in a crystalline cubic Ge2Sb2Te5 phase is found by PDF analysis. By adding Sb, the crystalline cubic phases coexist with two types of amorphous phases, depending on the quenching temperature. One has a first sharp diffraction peak similar to the amorphous Sb at Q ∼1.1 Å−1. Another has a new peak at Q ∼0.74 Å−1. Based on our crystal structure analyses, the composition of the new amorphous phase was estimated to be about Ge7Sb8Te10. The composition of the crystalline solid was also found to be different from the matrix, resulting in the nucleation dominated crystal growth in this system.