Influence of vacancies on the static and dynamic properties of monoatomic liquids
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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 R-ns is characterized by the period of time t(osc) = 6.07 x 10(-13) s in l-Pb and t(osc) = 7.88 x 10(-13)s in l-Ge. In the defect substructure the appearance of vacancy stipulates the shift of its nearest neighbours (Z(1)) towards the next nearest neighbours (Z(2)) for a distance DeltaR which is estimated as DeltaR = 0.67Angstrom, in l-Pb and 0.99Angstrom in l-Ge. The I 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 = Z(1) + Z(2) is found to be Z = 24 in l-Pb and Z = 18 in l-Ge. The jump of vacancy for a distance I= R-ns + 2DeltaR occurs during the time interval which is at the melting point t(D) = 1.99,X 10(-11)s in l-Pb and t(D) = 1.39 x 10(-11) s in l-Ge. The displac...ement of vacancy nearest neighbours for a distance DeltaR occurs during the time t(r) = 2.17 x 10(-12)s in l-Pb, and t(r) = 2.87 x 10(-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 DeltaE = 0, the relaxation entropy should be DeltaS(r) = DeltaE/T = 0. The results of this work, and particularly the activation entropy obtained as DeltaS(SD) = -4.20 k in l-Pb and DeltaS(SD) -3.66 k in,l-Ge support the self-diffusion in these liquids as an activation process. (C) 2003 Elsevier Science B.V. All rights reserved.