Phase transitions in quasicrystallineAl6CuMg4

Calorimetric and electron diffraction studies reveal that the quasicrystalline-to-crystalline phase transition in ${\mathrm{Al}}_6$Cu${\mathrm{Mg}}_4$ is endothermic, in contrast to the exothermic crystallization in quasicrystalline Al-Mn reported earlier. This finding indicates that the stability of certain quasicrystalline phases may be much larger than that of the Al-Mn system. This finding is in agreement with the prediction based on quantum structural diagrams. From a kinetic study the activation energy of this phase transition was found to be 260 kJ/mole.