Unmixing of binary alloys by a vacancy mechanism of diffusion: a computer simulation |
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Authors: | Khwaja Yaldram Kurt Binder |
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Institution: | (1) Institut für Physik der Universität, Staudinger Weg 7, W-6500 Mainz, Germany;(2) Present address: Pakistan Institute of Nuclear Science and Technology (PINSTECH), P.O. Nilore, Islamabad, Pakistan |
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Abstract: | The initial stages of phase separation are studied for a model binary alloy (AB) with pairwise interactions
AA
,
AB
,
BB
between nearest neighbors, assuming that there is no direct interchange of neighboring atoms possible, but only an indirect one mediated by vacancies (V) occurring in the system at a concentrationc
v
and which are strictly conserved, as are the concentrationsc
A
andc
B
of the two species.A-atoms may jump to vacant sites with jump rate
A
, B-atoms with jump rate
B
(in the absence of interactions). Particular attention is paid to the question to what extent nonuniform distribution of vacancies affects the unmixing kinetics. Our study focuses on the special case
A
=
B
on a square lattice, considering three different choices of interactions with the same =
AB
– (
AA
+
BB
)/2: (i)
AB
=,
AA
=
BB
= 0; (ii)
AA
= 0,
AA
=
BB
; = ; (iii)
AB
=
BB
= 0,
AA
= –2. We obtain both the time evolution of the structure factorS(k,t) following a quench from infinite temperature to the considered temperature, and the timedependence of the mean cluster size and the various neighborhood probabilities of a vacancy. While in case (i) forc
V
0.16 the distribution of vacancies in the system stays nearly random, in case (ii) the vacancies cluster in theA-B interfacial region, and in case (iii) they get nearly completely expelled from theA-rich regions. While phase separation proceeds in case (i) only slightly faster than in case (ii), a significant slowing down of the relaxation is observed for case (iii), which shows up in a strong reduction of the effective exponents describing the growth. |
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Keywords: | |
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