Temperature- and Pressure-Induced Polyamorphic Transitions in AuCuSi Alloy

Temperature-induced liquid-liquid phase transition (LLPT) and pressure induced amorphous-amorphous phase transition (AAPT) have never been simultaneously reported in any single metallic system. In an Au55Cu25Si20 alloy, however, we discovered a temperature-induced LLPT by detecting reversible lambda-anomalies of the thermal expansion coefficient between two liquid states at ambient pressure, while a pressure-induced AAPT in Au55Cu25Si20 metallic glass (MG) occurs upon compression at ambient temperature. Both LLPT and AAPT are reversible with a hysteresis in temperature and pressure, respectively. Using molecular dynamics simulations and synchrotron X-ray techniques, we elucidate structural differences in both low- and high-pressure Au55Cu25Si20 MG phases and low- and high temperature Au55Cu25Si20 liquid phases. Electronic transfer between Si and Au or/and Cu atoms occurs in both temperature-induced LLPT and pressure-induced AAPT in the Au55Cu25Si20 alloy.