Local Atomic Structures in Amorphous and Quasicrystalline Zr 70 Ni 10 Pt 20 and Zr 80 Pt 20 Alloys by the Anomalous X-ra
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Local Atomic Structures in Amorphous and Quasicrystalline Zr70Ni10Pt20 and Zr80Pt20 Alloys by the Anomalous X-ray Scattering Method Eiichiro Matsubara, Takahiro Nakamura1, Masaki Sakurai, Muneyuki Imafuku2, Shigeo Sato2, Jyunji Saida2 and Akihisa Inoue Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan 1 Department of Material Science, Graduate School, Tohoku University, Sendai, 980-8579, Japan 2 Inoue Superliquid Glass Project, ERATO, Japan Science and Technology Corporation (JST), Sendai 982-0807, Japan ABSTRACT Local atomic structures around Zr and Pt in a quasicrystalline Zr80Pt20 alloy, and amorphous and quasicrystalline Zr70Ni10Pt20 alloys have been determined by the anomalous x-ray scattering (AXS) method. A distinct prepeak observed in an intensity profile of the amorphous Zr70Ni10Pt20 alloy indicates existence of strong chemical short-range order (CSRO) clusters in the amorphous phase. Total coordination numbers around Zr and Pt in a nearest neighbor region in both alloys have been evaluated. The values around Pt are almost equal to 12 in the amorphous and quasicrystalline states suggest formation of icosahedral clusters around Pt. Some of crystalline structures formed from the quasicrystalline phases by annealing consist of icosahedral clusters of Zr and Ni atoms, or polyhedral clusters of Zr and Pt atoms similar with icosahedral clusters. The present result appears to support that the phase transformation from the amorphous to the crystal through the quasicrystal is explained by the icosahedral CSRO clusters in the amorphous and quasicrystalline states.
INTRODUCTION Inoue et al.[1] have found one of typical bulk metallic glasses in Zr-Al-TM (TM=Mn, Fe, Co, Ni and Cu) systems that include neither noble metals nor lanthanide metals. Recently, in some multi-component Zr-based alloys, formation of an icosahedral quasicrystalline phase has been reported [2,3]. It is sensitively affected by a cooling rate or oxygen content [4,5]. Chen et al. [6] found that addition of Ag improves formation of a quasicrystalline phase in amorphous Zr-based alloys. Reproducible formation of the quasicrystalline phase has been confirmed in the amorphous Zr-Al-Ni-M (M=Ag, Pd, Au and Pt) alloy [7-8]. An icosahedral quasicrystalline phase was confirmed as a primary precipitation phase in melt-spun Zr70Ni10M20 (M=Pd, Au and Pt) ternary metallic glasses with two-stage crystallization process [9]. The possibility of existence of icosahedral CSRO in the amorphous state due to large negative heats of mixing for Zr-M pairs was mentioned for formation of nanometer-sized quasicrystals. According to AXS measurements at Zr and Pt absorption edges in an amorphous Zr70Al6Ni10Pt14 alloy, presence of some CSRO clusters around Pt atoms was pointed out [10]. Saida et al. [11] also found a nanometer-sized icosahedral quasicrystalline phase even in a rapidly solidified Zr80Pt20 binary alloy. In the present study, coordination numbers and atomic distances in a near neighbor region around Pt as well as Zr in amorphous and quasi
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