NegativeP−Tslopes characterize phase change processes: Case of the Ge1Sb2Te

Abstract

The crystalline, liquid and amorphous phase stabilities and transformations of the Ge 1 Sb 2 Te 4 (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 solidstate 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.

Breakdown of the Stokes-Einstein relation above the melting temperature in a liquid phase-change material

“…The latter can be justified from the fact that a positive volume change upon melting (i.e. positive Clapeyron slope) is reported(21,71) at ambient pressure while the high-pressure V-shape Tm-curve (and open diamonds) accords with the work of Sen and coworkers(72,73). Therefore, the ambient pressure isobar crosses a Widom line (dashed bold line) with a LLCP nearby.…”

“…P-T metastable liquid phase diagram conjectured for Ge 1 Sb 2 Te 4 , in analogy to that of water (inset). References (50)(51)(52)(53)(54)(55)(56)(57)(58)(59)(60)(61)(62)(63)…”

Nature of metastable amorphous-to-crystalline reversible phase transformations in GaSb

“…5 In fact, the stable and metastable phase equilibria in Si display a number of interesting characteristics that form a universal pattern for other tetrahedral (e.g., Ge, III-V compounds) and non-tetrahedral (e.g., pseudo-binary "GST" phase change compounds along the GeTe-Sb 2 Te 3 join) semiconductors. [6][7][8][9][10][11][12] The stable phase equilibria have the following characteristics:…”