L1<SUB>2</SUB>型構造の規則化における異位相VARIANTの発展過程

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タイトル別名
  • Evolution of Off-Phase Variants in Ordering of L1<SUB>2</SUB> Type Structure
  • L12型構造の規則化における異位相VARIANTの発展過程
  • L12ガタ コウゾウ ノ キソクカ ニ オケル イイソウ VARIANT ノ

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A theory is displayed to describe the development of off-phase variants in the L12 ordering in alloys such as Cu3Au. In this type of order, there exist four distinct crystallographic variants, anyone of which is displaced from the other three by one of the three primitive translations of an fcc structure. In the present model, the fcc lattice is decomposed into four simple cubic sublattices, where the atomic arrangement in the long range order is represented by three independent order parameters. These parameters are related to the corresponding structure factors for superstructure reflections. The state of order of atomic arrangement in the system is defined by a point in the three dimensional Euclid space spanned by these three order parameters. The actual L12 order structure is given by anyone of the four tips of a regular tetrahedron around the origin, which represents the disordered state. A simple free energy of the Landau type is introduced as a function of these order parameters up to their fourth powers. The free energy includes two parameters depending on temperature, and the equilibrium values for the L12 order parameters are determined by those as functions of the temperature. Below the transformation temperature, the disordered state is unstable against ordering. Small disturbances in the atomic arrangement cause the system to change their state of order following a path in the order space, and to fall into one of the four minimum points of the free energy. In order to investigate the dynamical behavior of the ordering, the surface and the interfacial energies are introduced between the ordered phase and the disordered one, or between any pair of the ordered variants. The equations of motion for the space-time evolution of the order state are derived by the TDGL (time-dependent Ginzburg-Landau) method. The PC simulation for the pattern formation of ordering with multiple variants was performed successfully.

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  • 日本金属学会誌

    日本金属学会誌 61 (2), 113-119, 1997

    公益社団法人 日本金属学会

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