Icosahedral AlCuFe quasicrystal at high pressure and temperature and its implications for the stability of icosahedrite

Abstract

The first natural-occurring quasicrystal, icosahedrite, was recently discovered in the Khatyrka meteorite, a new CV3 carbonaceous chondrite. Its finding raised fundamental questions regarding the effects of pressure and temperature on the kinetic and thermodynamic stability of the quasicrystal structure relative to possible isochemical crystalline or amorphous phases. Although several studies showed the stability at ambient temperature of synthetic icosahedral AlCuFe up to ~35 GPa, the simultaneous effect of temperature and pressure relevant for the formation of icosahedrite has been never investigated so far. Here we present in situ synchrotron X-ray diffraction experiments on synthetic icosahedral AlCuFe using multianvil device to explore possible temperature-induced phase transformations at pressures of 5 GPa and temperature up to 1773 K. Results show the structural stability of i-AlCuFe phase with a negligible effect of pressure on the volumetric thermal expansion properties. In addition, the structural analysis of the recovered sample excludes the transformation of AlCuFe quasicrystalline phase to possible approximant phases, which is in contrast with previous predictions at ambient pressure. Results from this study extend our knowledge on the stability of icosahedral AlCuFe at higher temperature and pressure than previously examined, and provide a new constraint on the stability of icosahedrite.

X-ray diffraction study of the icosahedral AlCuFe quasicrystal at megabar pressures

“…The XRD profile is completely consistent with that of i-AlCuFe QC previously reported [11]. We detected additional peaks due to a small amount of AlFe 3 which was observed in the previous study as well [5]. The AlFe 3 commonly occurs as an accessory compound during the procedure for synthesis of i-AlCuFe QC.…”

“…The five characteristic peaks from the i-AlCuFe QC persist up to 104 GPa, indicating that the structure does not undergo drastic changes within the experimental pressure range. In the previous high-pressure and high-temperature study on the i-AlCuFe QC [5], the peaks derived from the AlFe 3 were disappeared at 973 K and 5 GPa. At ambient temperature, on the other hand, the peaks from the AlFe 3 are completely disappeared above 34 GPa.…”

“…The AlFe 3 commonly occurs as an accessory compound during the procedure for synthesis of i-AlCuFe QC. The presence of AlFe 3 can be neglected taking into consideration the previous experimental result of high-pressure and high-temperature study on i-AlCuFe QC [5]. Diffractions corresponding to the i-AlCuFe QC are marked with the Cahn indices (N, M) [16,17] on the respective peaks in Fig.…”

“…The six-dimensional lattice parameter, a 6D , is useful as a QC structural indicator. It is defined by the following equation [5].…”

“…The exotic assemblage makes it extremely complex to understand how the natural QCs were formed. A recent experimental study investigated the thermodynamic stability of icosahedral (i)-AlCuFe QC and showed that the i-AlCuFe QC remains its structure up to 5 GPa and 1673 K [5]. To date, a few experimental studies on the high-pressure behavior of i-AlCuFe QC at ambient temperature have been published [6,7,8].…”