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Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (Received 13 August 1990; accepted 13 November 1990) The energies and configurations of interstitials and vacancies in the ordered compounds CuTi and CuTi2 were determined using atomistic simulation with realistic embedded-atom potentials. The formation energy of an antisite pair was found to be 0.385 and 0.460 eV in CuTi and CuTi2, respectively. In both compounds, the creation of a vacancy by the removal of either a Cu or Ti atom resulted in a vacant Cu site, with an adjacent antisite defect in the case of the Ti vacancy. The vacant Cu site in CuTi was found to be very mobile within two adjacent (001) Cu planes, with a migration energy of 0.19 eV, giving rise to two-dimensional migration. The vacancy migration energy across (001) Ti planes, however, was 1.32 eV, which could be lowered to 0.75 or 0.60 eV if one or two Cu antisite defects were initially present in these planes. In CuTi2, the vacancy migration energy of 0.92 eV along the (001) Cu plane was significantly higher than in CuTi. The effective vacancy formation energies were calculated to be 1.09 eV and 0.90 eV in CuTi and CuTi2, respectively. Interstitials created by inserting either a Cu or Ti atom had complicated configurations in which a Cu (111) split interstitial was surrounded by two or three Ti antisite defects. The interstitial formation energy was estimated to be 1.7 eV in CuTi and 1.9 eV in CuTi2.

I. INTRODUCTION

The properties of point defects have been investigated for over forty years using experimental and theoretical techniques, motivated by the fact that they play an important role in many technologically important phenomena. For many materials, particularly bcc and fee metals, a generally accepted picture of point defect properties has emerged.1'2 In the typical case of copper, for example, interstitials are found to form (100) dumbbell configurations having a high formation energy (2.2 ± 0.7 eV3) and a low migration energy (0.12 eV4). Interstitials are highly mobile and can mutually recombine with vacancies, annihilate at extended sinks, bind to impurities, or cluster.2 Vacancies, on the contrary, have a lower formation energy (1.31 eV5) and a higher migration energy (0.76 eV6) than do interstitials, and are thus immobile below about 275 K, the Stage-Ill temperature in copper.1 These characteristics of point defects in copper, i.e., highly mobile interstitials and less mobile vacancies, can be generalized to many other pure fee and bcc metals. Our understanding of point defects in concentrated alloys and intermetallic compounds, on the other hand, is poor, despite the fact that many of these compounds a)

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are technologically more important than pure metals. Investigation of point defect properties of intermetallic compounds is experimentally difficult because of the problem of distinguishing from among the plethora of possible point defect types (e.g., antisite defects, vacancies, and interstitials on different sub