Influence of vacancies on the static and dynamic properties of monoatomic liquids

The structure of monoatomic liquids is assumed to consist of the normal substructure and defect substructure. The oscillatory motion of atoms in the normal substructure with the nearest-neighbour distance Rns is characterized by the period of time tosc=6.07x10-13 s in l-Pb and tosc=7.88x10-13 s in l-Ge. In the defect substructure the appearance of vacancy stipulates the shift of its nearest neighbours (Z1) towards the next nearest neighbours (Z2) for a distance ΔR which is estimated as ΔR=0.67 A in l-Pb and 0.99 A in l-Ge. The concentration of vacancies in both liquids is determined from the experimental static structure factor S(q). The sum of the first and second vacancy neighbours Z=Z1+Z2 is found to be Z=24 in l-Pb and Z=18 in l-Ge. The jump of vacancy for a distance l=Rns+2ΔR occurs during the time interval which is at the melting point tD=1.99x10-11 s in l-Pb and tD=1.39x10-11 s in l-Ge. The displacement of vacancy nearest neighbours for a distance ΔR occurs during the time tr=2.17x10-12 s in l-Pb, and tr=2.87x10-12 s in l-Ge. The time interval 10-12 s was erroneously attributed to the self-diffusive motion of liquid particles. Since the energy gain of this process is ΔE=0, the relaxation entropy should be ΔSr=ΔE/T=0. The results of this work, and particularly the activation entropy obtained as ΔSSD=-4.20 k in l-Pb and ΔSSD=-3.66 k in l-Ge support the self-diffusion in these liquids as an activation process