Negative P-T slopes characterize phase change processes: Case of the Ge1Sb2Te4 phase change alloy

The crystalline, liquid and amorphous phase stabilities and transformations of the Ge₁Sb₂Te₄ (GST124) alloy are investigated as a function of pressure and temperature using synchrotron diffraction experiments in a diamond anvil cell. The results indicate that the solid-state amorphization of the cubic GST124 phase under high pressure may correspond to a metastable extension of the stability field of the GST124 liquid along a hexagonal crystal-liquid phase boundary with a negative P-T slope. The internal pressures generated during phase change are shown to be too small to affect phase stability. However, they may be important in understanding reliability issues related to thermomechanical stress development in phase change random access memory structures.