Metastable phase formation in an immiscible Cu-Ta system studied by ion-beam mixing, ab initio calculation, and molecular dynamics simulation

Abstract

Ion-beam mixing experiments show that amorphous phases are formed in the Cu 70Ta 30, Cu 65Ta 35, Cu 60Ta 40, and Cu 50Ta 50 multilayered samples, while a crystalline structure is retained in the Cu 75Ta 25 sample. These results suggest that the composition limit for forming an amorphous phase is around 30 at.% Ta, which confirms the same value of 30 at.% Ta predicted by recent atomistic modeling. For the metastable crystalline Cu 75Ta 25 phase, ab initio calculations identify its relatively stable structure to be L1 2 (fcc type) and determine some associated physical properties, which agree well with those derived from a proven realistic Cu-Ta potential through molecular dynamics simulations. Interestingly, an fcc Cu 75Ta 25 phase is indeed observed in ion-beam mixing experiments and its lattice constant determined by diffraction analysis matches well with those from theoretical calculations.