The structural phase transformation and elastic instability in F.C.C. metals

A simple analytical embedded-atom potential model with four adjustable parameters is presented. This potential and several other potential models (including a pair potential) are used to study structural phase transformation and theoretical strength of f.c.c. metals Al, Ag, Au, Cu, Ni, Pd, Pt under [100] uniaxial loading. It is found that due to the dependence on the elastic constants c11, c12, c22, and c23 the theoretical strengths calculated are independent of the potential models used for each one of these metals and the result for the metal Cu is in agreement with the experimental value. However, due to c23 = c14 the predictions of the phase transformations by the pair potential are different from those by embedded-atom potentials. In the pair potential calculations, like the previous ones, the unstressed b.c.c. phase is found to be stable. In embedded-atom potential calculations the stress-free b.c.c. phase is found to be unstable by our present potential model or that of Voter and Chen, though the potential of Rosato et al. gives a b.c.c. phase favourable over the f.c.c. phase for the metals Ag, Au, Cu and Ni. The energy differences of f.c.c.-b.c.c. phases predicted by our present potential are comparable with those by the first-principles calculations for all these metals considered. Also, an embedded-atom potential, where its embedding energy as a function of electron density becomes negatively defined, may give an erroneous prediction for the stability of the b.c.c. phase in these f.c.c. metals. (orig.)