Bulk materials are required which combine useful characteristics of their components such as light, strong, ductile, and hard. In other cases certain thermoelectric parameters are aimed at. We discuss briefly the electronic origins of these properties.

For the above purpose Al-TM systems are promising candidates (Al aluminum, TM d transition metal). Aluminum promotes the nearly-free electron character of the band states whereas the TM atoms are capable pinning electrons by strong scattering. Hence. the atomic structures of Al-TM alloys and the above electron fine tuning must be mutually dependent. A few typical structural peculiarities are presented.

It took fifty years to understand the main features of the Al-TM interplay in such spd electron phases. We outline the fundamental ideas.

There are Al-TM alloys which behave only marginally metallic. Anyway this is due to electronic interference. However, a detailed analysis reveals fundamental differences between periodic and aperiodic systems. Nevertheless we show that aperiodic quasicrystals can be modeled upon scaling spectral properties of their periodic approximants.