A New Type of Long Period Superlattice with Hexagonal Symmetry in Au-Cd Alloys

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概要

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• The existence of a new type of long period superlattice having hexagonal symmetry, whose period is determined by the critical contact of the Brillouin zone boundaries with the Fermi surface, has been established. The ordering of the atoms on the close packed hexagonal plane of these structures is derived from that of the A_3B type (Cu_3Au type) structure, but the long period is produced in the basal plane by the existence of antiphase boundaries in three directions perpendicular to the close packed plane and making 120° with each other, thus creating the hexagonal symmetry. The stacking of the close packed layers is of either the 2H or 4H type. The size of this hexagonal unit cell is found to be between seven and nine times as large as that of the hexagonal unit cell of the disordered close packed lattice, these limiting cases being called the 7a_0 structure and the 9a_0 structure respectively. Significantly, the period of this structure is found to respond to a change of e/a in a fashion similar to that found in the one dimensional long period superlattice, which has been investigated in detail. In the case of the Au-Cd alloys, the stacking is of the 2H type and the 7a_0 structure is identified as Au_<72>Cd_<26> with space group P6_3/mmc, and the 9a_0 structure as Au_<42>Cd_<12> with P6_3/mcm. The geometry of the Brillouin zone structure indicates that the structure is stabilized by creating superlattice Brillouin zone boundaries at the flat part of the Fermi surface (in the <110> directions in the case of the fcc structure), as in the case of the one dimensional long period superlattice. Examples of these new structures are found, other than in the Au-Cd alloys reported here, in Au-Mg alloys, Cu-Sb alloys, etc. near the A_3B composition range. These structures are usually found among the long period stacking variants of a one dimensional long period superlattice with non variable period (M=1, M=2, etc.), occurring in these alloys.

• 東北大学の論文

著者

• HIRABAYASHI M.

  The Research Institute for Iron, Steel and Other Metals, Tohoku University

• Toth R.

  Scientific Laboratory Ford Motor Company

• HIRAGA K.

  The Research Institute for Iron, Steel and Other Metals

• Ino N.

  The Research Institute For Iron Steel And Other Metals Tohoku University

• YAMAGUCHI S.

  The Research Institute for Iron, Steel and Other Metals, Tohoku University

• SATO H.

  Scientific Laboratory, Ford Motor Company

• Hiraga K.

  The Research Institute For Iron Steel And Other Metals

• Yamaguchi S.

  The Research Institute for Iron, Steel and Other Metals

関連論文

• Stress-Strain Analysis of Single Cubic Crystals and Its Application to the Ordering of CuAu I : Paper II
• An Experimental Study on the Ordered Alloy Ni_2Cr
• Age-Hardening of Aluminium-Gold Alloys
• Constitution of the Indium-Rich Portion of the Indium-Magnesium System
• A New Type of Long Period Superlattice with Hexagonal Symmetry in Au-Cd Alloys
• Confirmation of Existence of Cu_3Au II Using Thin Films
• Confirmation of Existence of CU_3Au II Using Thin Films
• Study on Anti-Phase Domains in Cu_3Au by Means of Electron Diffraction and Electron Microscopy
• Study on Anti-Phase Domains in Cu_3Au by Means of Electron Diffraction and Electron Microscopy
• Vacancy Ordering in Vanadium Carbides Based on V_6C_5
• Long-Period Ordered Structures in the Quasi-Binary CO_3V-Ni_3V Alloy

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