| Empirical embedded atom method (EAM) type potentials were developed and applied in molecular dynamics (MD) studies of amorphous copper-zirconium. The EAM is extended to the HCP metal, Zr where the non-ideal c:a ratio and the elastic responses, including contributions from internal degrees of freedom, are incorporated in the fitting procedure. For both metals, simple functional forms are assumed for the pair interaction, atomic electron density and embedding function. The functions are parametrized by fitting to experimental data: cohesive energy, equilibrium lattice constants, single crystal elastic constants and vacancy formation energy. An equation of state of the form proposed by Rose (Rose, Smith, Guinea and Ferrante 1984) is used to reproduce the pressure dependence of the cohesive energy. Dimer data and a high energy sputtering potential are also reproduced to extend the range of validity of the potential into regions of very high and low electron density. The multicomponent potential is determined and applied in simulations of amorphous Cu{dollar}sb{lcub}x{rcub}{dollar}Zr{dollar}sb{lcub}100-x{rcub}{dollar}. Melt quenching of a bulk liquid is simulated by isobaric, step-wise cooling at a rate of 4.5 {dollar}times{dollar} 10{dollar}sp{lcub}12{rcub}{dollar}K/s. Sharp peaks in the heat capacity as a function of temperature were observed indicating the occurrence of a structural relaxation which serves to lower the free energy of the system. Detailed structural analysis of CU{dollar}sb{lcub}50{rcub}{dollar}Zr{dollar}sb{lcub}50{rcub}{dollar} shows the relaxation corresponds to an increase in icosahedral ordering. The relaxation is observed at high temperature, while the system is still in equilibrium but the relaxation becomes slower at lower temperature and eventually occurs on the same timescale as the cooling at which point the system then drops out of equilibrium. At low temperature, there is an additional structural relaxation which appears to be a reversible, strain-related process. Simulated sputter deposited amorphous Cu{dollar}sb{lcub}50{rcub}{dollar}Zr{dollar}sb{lcub}50{rcub}{dollar} films show predominantly icosahedral ordering, to an even greater extent than observed in analogous liquid quenched films. In both systems, the observed icosahedra are found to be chemically ordered with central Cu atoms preferring Zr-rich coordination. The icosahedra are also found to be clustered, rather than evenly distributed, often interpenetrating or sharing a face. |
