First-Principles Prediction of Short-Range Order in Alloys
Solid state alloys at high temperatures often
undergo a phase transition to a disordered arrangement of the
constituent atoms. The arrangement is not random, however, but
may exhibit some degree of short-range order, i.e., the
excess probability of finding certain pairs of atoms relative
to random statistics. For the first time, ``state-of-the-art''
first-principles calculations including the effects of atomic
displacements have been extended to high
temperatures, and the resulting short-range order predicted.
The short-range order has been predicted for a variety of
transition metal and semiconductor alloys.
The excess pair probabilities associated with
short-range order are also a physically measurable
effect, and we have compared our parameter-free calculations
with experimental measurements, finding excellent agreement.
Our calculations have led to an increased understanding of
ordering properties in these alloys.
Many transition metal alloy systems are currently being considered
as a new class of materials for high-temperature applications.
In many cases these applications have been limited to date, however,
oftentimes due to a lack of fundamental understanding of the
materials properties. Also, in many semiconductor alloys, the
degree or extent of ordering is not even known experimentally.
The current theoretical calculations demonstrate that ordering
processes in alloys may be understood and even predicted (without
reference to any experiment) on a fundamental, microscopic
level. The theoretical predictions are shown to be highly
accurate by comparing with experimental measurements for transition
metal alloys, for which an abundance of experimental data exists.
These calculational tools are not specific to transition metals,
however, thus opening the door to calculations of ordering in
the highly technologically important semiconductor alloys, where
there exists very little or no experimental data.
Selected References
-
C. Wolverton, V. Ozolins, and Alex Zunger
``First-principles theory of short-range order in
size-mismatched metal alloys: Cu-Au, Cu-Ag, and Ni-Au''
Phys. Rev. B - in press, 1998.
-
C. Wolverton and A. Zunger,
``Ni-Au: A Testing Ground for Theories of Phase Stability''
Comp. Mat. Sci. 8, 107 (1997).
-
C. Wolverton, A. Zunger, and B. Schonfeld,
``Invertible and Non-Invertible Ising Alloy Problems''
Solid State Commun. 101, 519 (1997).
-
C. Wolverton and A. Zunger,
"First principles theory of short range order,
electronic excitations, and spin polarization in Ni-V and Pd-V
alloys",
Phys. Rev. B 52, 8813 (1995).
-
Z. -W. Lu, D. B. Laks, S. -H. Wei, and A. Zunger,
"First-Principles Simulated Annealing Study of Phase
Transitions and Short Range Order in Transition Metal and
Semiconductor Alloys",
Phys. Rev. B 50, 6642 (1994).
For more references on this topic, please see the
list of short-range
order publications, or for references on all topics, go to the
publications database.
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Last updated: January 9, 1998