Pressure Effects on the Transport and Structural Properties of Metallic Glass-Forming Liquid

Transport and structural properties of metallic glass-forming liquid Cu_50Zr_50 are investigated by molecular dynamics simulation, under high pressures from 1 bar to 70 GPa. The following results have been obtained: (i) reversals of component diffusion coefficients (D_\rm Cu and D_\rm Zr) are observed at the reversion pressure. At low pressures below the reversion pressure, D_\rm Cu/D_\rm Zr decreases from about 1.4 to 1.0. At high pressures above the reversion pressure, D_\rm Cu/D_\rm Zr decreases more rapidly from 1.0 to about 0.7. (ii) Component diffusion coefficients decay exponentially with pressure up to reversion pressure, then the strength of the exponential dependence changes, while the pressure-dependent behavior of viscosity can be well described by a single exponential relation over the full range of pressure. (iii) The Stokes–Einstein relation (SER) works well at low pressures and starts to be violated at the breakdown pressure. For glass-forming liquid Cu_50Zr_50 along the 2000 K isotherm, the breakdown pressure equals the reversion pressure of component diffusion coefficients and is about 35 GPa. (iv) The pressure dependences of the ratio between component diffusion coefficients can be used to predict the breakdown pressure of SER along isotherm. The validity of SER and the reversals of component diffusion coefficients are found to be related to the pressure dependence of the relative total fractions of predominant Voronoi polyhedrons around individual components.