Dynamics of Atomic Ordering in Bulk and Thin Film Intermetallic Alloys: A Complementary Approach to Atomic Migration
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Dynamics of Atomic Ordering in Bulk and Thin Film Intermetallic Alloys: A Complementary Approach to Atomic Migration W. Pfeiler1, W. Püschl1, Ch. Issro2, R. Kozubski3, and V. Pierron-Bohnes4 1
Dynamics of Condensed Systems, Faculty of Physics, University of Vienna, Strudlhofgasse 4, 1090 Vienna, Austria 2 Department of Physics, Faculty of Science, Burapha University, Chonburi, 20131 Thailand 2 Interdisciplinary Centre for Materials Modelling, M. Smoluchowski Institute of Physics, Jagellonian University, Reymonta 4, 30-059 Cracow, Poland 3 IPCMS-GEMME, CNRS-ULP, 23 rue du Loess, BP 43, 67034 Strasbourg Cedex 2, France ABSTRACT One of the foremost challenges in today’s materials science is the design and development of materials with physical properties customized for technical application. Due to their excellent corrosion resistance and their advantageous mechanical and in many cases also magnetic properties, intermetallic alloys are among the most important materials of the 21st century. Most of their outstanding qualities are linked to long-range order, the fact that unlike atoms are preferred as neighbours, which then segregate to different sublattices. In most intermetallics atomic order persists up to rather high temperatures, if not up to melting. However, connected with the entropy gain, the degree of order depends on temperature and thereby the stability of the designed beneficial materials properties is affected. By monitoring changes in the degree of atomic order an access to atom migration is gained, which is complementary to the usual diffusion experiments, where the degree of order is not changed on average. It is shown in this review on some selected examples how an adequate thermal treatment of the samples in combination with the experimental approach gives detailed information on atom jump mechanisms and structural changes, especially if experiment is combined with up-to-date kinetic Monte Carlo simulations. INTRODUCTION In ordered alloys, for example in intermetallics, the alloy atoms, due to a high attractive interaction between unlike atoms, are not distributed at random over the lattice positions; a preferential distribution of each kind of atom on specific sublattices of the crystal lattice is observed, leading to certain superstructures. A strict correlation between the different kinds of alloy atom and specific lattice positions for thermodynamic reasons is however maintained at 0 K only; it decreases with increasing temperature in a characteristic manner. Above the orderdisorder transition temperature TO/D, which in the cases of directly ordering alloys may be even higher than the melting temperature Tm, this ordering tendency stops and the alloy atoms are then distributed randomly over the possible sites of the crystal lattice. Actually, a slight local ordering tendency (short-range order (SRO)) in many cases remains [1,2] and the completely random atomic arrangement is a high-temperature limit. It is obvious that this effect of long-range order (LRO) has essential consequences
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