Temperature- and Pressure-Induced Polyamorphic Transitions in AuCuSi Alloy

Abstract

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 Au$_{55}$Cu$_{25}$Si$_{20}$ alloy, however, we discovered a temperature-induced LLPT by detecting “reversible λ-anomalies” of the thermal expansion coefficient between two liquid states at ambient pressure, while a pressure-induced AAPT in Au$_{55}$Cu$_{25}$Si$_{20}$ 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 Au$_{55}$Cu$_{25}$Si$_{20}$ MG phases and low- and high-temperature Au$_{55}$Cu$_{25}$Si$_{20}$ liquid phases. Electronic transfer between Si and Au or/and Cu atoms occurs in both temperature-induced LLPT and pressure-induced AAPT in the Au$_{55}$Cu$_{25}$Si$_{20}$ alloy