Irradiation-induced ordering in Pt-Cu alloy focusing on Pt 7 Cu
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Irradiation-induced ordering in Pt-Cu alloy focusing on Pt7Cu T. Nagase1, 2, Y. Seno1, H. Yasuda1,2, and H. Mori1 1 Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, 7-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan. 2 Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan. ABSTRACT The existence of Pt7Cu ordering phase (intermetallic compound) was investigated by ab initio calculations and high voltage electron microscopy (HVEM) focusing on irradiationinduced ordering. The Pt7Cu ordering phase (cF32, prototype Ca7Ge) was predicted at 0 K through density functional theory (DFT), and using cluster expansion (CE) method and grand canonical Monte Carlo (GCMC) simulation, the ordering temperature of fcc-based Pt7Cu ordering phase was estimated to be above room temperature. The formation of Pt7Cu ordering phase was confirmed by a short-time irradiation for 3.6×103 s at 600 K. MeV electron irradiation can reduce drastically the annealing time for the ordering in the Pt-Cu alloy system, indicating that the combination of the prediction by ab initio calculations and HVEM can offer the unique opportunity to investigate the existence of ordering phase in alloys. INTRODUCTION Pt-Cu alloys have been of great interest over the past few years because of their potential application as an alternative to pure-Pt, and Pt-group catalysts [1, 2]. The formation of Pt-Cu ordering phases is important for designing the Pt-Cu alloy system. Figure 1 shows the typical PtCu binary phase diagram focusing on Pt-Cu ordering phases [3, 4]. The Pt-Cu binary system consists of a continuous solid solution phase (fcc phase) at high temperature regions, and several ordered phases at low temperatures. Subramanian et al. [3] reported various ordering phases as shown in Figure 1a, and Abe et al. [4] attempted thermodynamic assessment in Pt-Cu alloy system based on the assumptions of liquid, A1 (disordered fcc), L12-PtCu3, and L11-PtCu stable phases, and L12-Pt3Cu and L11-PtCu metastable phases in the Pt-Cu alloy system as shown in Figure 1b. The structure of Pt-Cu ordering phases were also predicted with ab initio calculations [5-7], and investigated by TEM analysis [8], however, these reports have little agreement between the formation and structure of Pt-Cu ordering phases. In this study, we attempted to investigate the formation and structure of Pt-rich Pt-Cu
Figure 1. Typical Cu-Pt phase diagram focusing on Pt-Cu ordering phases given by (a) 1990, Subramanian et al. [3], and (b) 2006, Abe et al. [4]
ordering phases from slightly different angles of the irradiation-induced ordering by HVEM [912]. Fast-electron irradiation in metals leads to the displacement of constituent atoms, resulting in the formation of point defects. Accumulation of these defects can stimulate the destruction of the ordered atom arrangement, but can also enhance the ordering of disordered structures by radiation enhanced diffusion, resulting in the reduction of the a
