Experimental study of the electronic density of states in aluminium-based intermetallics

We report on an experimental investigation of the electronic density of states (DOS) in aluminium-based intermetallics by three experimental techniques: electrical resistivity, NMR spin–lattice relaxation and soft x-ray emission spectroscopy (SXES). The investigated samples were alloys of Al with transition elements Cu, Fe, Cr, Pd and Mn and sometimes also a small amount of B. The samples were structurally very different and included (1) regular periodic intermetallic compounds, (2) large-unit-cell intermetallics that are translationally periodic on the scale of several nanometres and exhibit local polytetrahedral order (like quasicrystals) on the scale of interatomic distances and (3) quasicrystals. Correlation analysis between the DOS parameters determined independently by the three techniques employed showed that the order of samples with decreasing metallic character was the same in all experiments. Quantitative evaluation of the DOS at E F has shown that in regular alloys the DOS is reduced to about 50% of the free-electron-like value in fcc Al metal, whereas the reduction becomes increasingly larger on going to large-unit-cell periodic solids and quasicrystals. Our results also demonstrate that low resistivities are accompanied by positive temperature coefficient (PTC) variation, whereas samples with large resistivity exhibit negative temperature coefficient (NTC). Samples with a resistivity of about 200 µΩ cm appear to be at a crossover from PTC to NTC resistivity, resulting in a temperature-compensated resistivity with essentially zero temperature coefficient. Magnetic properties of the samples are also presented.