Al p-like states in highly resistive icosahedral alloys

This letter presents a systematic study of Al p states in various icosahedral quasicrystals by means of absorption and emission x-ray spectroscopies. For the sake of comparison, crystals showing different degrees of icosahedral order are examined as well. Direct evidence is given for the first time that the metallic character attached to the constituent atoms tends to disappear in all stable Al-3d (4d and Sd) transition metal icosahedral quasicrystals known at present. The density of conduction states at the Fermi level and beyond (up to 3-5 eV) has indeed dramatically vanished in the icosahedral quasicrystals. In crystalline approximants the same effect is observed but to a much lesser extent. This effect is strongly related to the resistivity increase observed by electron transport measurements. A discussion of the results is proposed in the light of a recent model based upon a hierarchy of quantum wells.