Surface properties of the B2-based approximants in relation to quasicrystals

Quasicrystals and their approximants are Hume-Rothery compounds having similar valence electron concentrations. According to this new understanding of approximants, some B2 superstructures can be regarded as a special group of approximants. The present paper examines surface characteristics of this group of approximants synthesized by hot pressing. Friction coefficient, surface energy and hardness are analyzed and influences from factors such as valence electron concentration and Al3p partial density of states at the Fermi energy are discussed. Specifically, we show that samples containing the B2 structure and its superstructures exhibit a friction coefficient which decreases with increasing e/a and reaches minimum at 1.86, the value of the quasicrystal. Therefore, the B2-based approximants and quasicrystals belong to one group of phases whose surface properties are mainly determined by electronic structure characteristics rather than crystal structures.