Investigation on Ge_5-xSb_xTe₅ phase-change materials by first-principles method

The structure stability and chemical bonding of Ge_5-xSb _xTe₅ (x = 0, 1, 2) phase-change alloys were studied by ab initio calculations. By analyzing formation energies, density of states and electron localization function, we have shown that the chemical bonding character of Ge₄Sb₁Te₅ is quite similar to that of GeTe and hence a NaCl crystalline state is expected. The introduction of extra electrons by Sb in Ge₄Sb₁Te₅ and Ge ₃Sb₂Te₅ results in states at the Fermi Level. With increasing Sb contents as in Ge₃Sb₂Te₅, the chemical bonding becomes rather inhomogeneous.