Studies of phase stability mechanism in structurally complex gamma-brass alloys containing 52 atoms in the unit cell

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We have chosen Cu_5Zns and CuPAI_4 gamma-brasses containing 52 atoms in the unit cell as systems with relatively small number of atoms among structurally complex metallic alloy phases and clarified why they are stabilized at a particular electron concentration e/a=21/13 by performing the first-principles FLAPW band calculations. The present project has been conducted to extend the pioneering work above to gamma-brasses characterized by their own unique electronic structures.1. In the first year of 2005, we have synthesized the TM-Zn (TM=Ni, Pd, Co and Fe) gamma-brasses and made their detailed structure analysis by using the powder diffraction apparatus in the beamline BLO2B2, SPring-8 synchrotron radiation facility, Japan. The stability mechanism of these gamma-brasses was studied by performing the FLAPW band calculations.2. In the second year of 2006, we have synthesized the A1_8V_5 gamma-brass and made its detailed structure analysis by using the powder diffraction apparatus in the beamline BLO2B2, SPring-8 synchrotron radiation facility, Japan. The stability mechanism of the A1_8V_5 gamma-brass was studied by performing the FLAPW band calculations.3. In the final year of 2007, we have synthesized the Ag_5Li_8 gamma-brass and made its detailed structure analysis by using the powder diffraction apparatus in the beamline BLO2B2, SPring-8 synchrotron radiation facility, Japan. The stability mechanism of the Ag_5Li_8 gamma-brass was studied by performing the FLAPW band calculations.In conclusions, we revealed that the stabilization mechanism is not uniquely specified but is strongly system dependent, even though all. gamma-brasses studied are completely isostructural to each other. The present work clarified, for the first time, the presence of the limit to the applicability of the Hume-Rothery electron concentration rule for structurally complex alloy phases.