[S-MP42] Physics and Chemistry of Minerals

[SMP42-P13] Study on the stability of the Al_{65}Cu_{20}Fe_{15} icosahedral quasicrystal using Synchrotron X-ray diffraction method

*Sota TAKAGI¹, Atsushi KYONO² (1.College of Geoscience, School of Life and Environmental Sciences, University of Tsukuba, 2.Graduate School of Life and Environmental Sciences, University of Tsukuba)

Keywords:Al_{65}Cu_{20}Fe_{15} icosahedral quasicrystal, icosahedrite, stability, high pressure and high temperature, XRD

The stability of the Al₆₅Cu₂₀Fe₁₅ icosahedral quasicrystal at high pressure and high temperature has been investigated using synchrotron X-ray diffraction method. High pressure in situ XRD experiments ware performed up to 104 GPa, and high pressure and high temperature in situ XRD experiments ware performed at the pressure points of 11, 24, 33, 57, 67, 104 GPa up to temperature of about 2500 K. The high pressure experiments revealed that five characteristic XRD peaks of the Al₆₅Cu₂₀Fe₁₅ icosahedral quasicrystal remained up to 104 GPa at room temperature, while a new peak appeared at the point of d = 2.90 Å above 89 GPa. The six-dimentional lattice parameter, a_6D, was continuously contracted from 12.5 Å to 11.2 Å with pressure. The bulk modulus of the Al₆₅Cu₂₀Fe₁₅ icosahedral quasicrystal started to change around 70 GPa. This result suggested that the Al₆₅Cu₂₀Fe₁₅ icosahedral quasicrystal was transformed to high pressure phase at about 70 GPa. The high pressure and high temperature experiments showed that a different phase (high-temperature phase) occurs as a function of the temperature. The phase boundary between the Al₆₅Cu₂₀Fe₁₅ icosahedral quasicrystal and its high temperature phase was risen with pressure, such as 865 K at 11 GPa, 1402 K at 24 GPa, 1758 K at 33 GPa, 1963 K at 57 GPa, 2050 K at 67 GPa, 2080 K at 104 GPa. In a series of the study, the Al₆₅Cu₂₀Fe₁₅ icosahedral quasicrystal was melted completely only when it was heated to 2385 K at 11 GPa. From the present study, it was suggested that mineral icosahedrite (Al₆₃Cu₂₄Fe₁₃), the first natural-occurring quasicrystal, was formed at pressure range from 5 GPa to 70 GPa, and at temperature range from 1500 K to 2200 K. This study can be a clue to solve the question of where and how the icosahedrite was formed.