ANOMALOUS ELECTRONIC BEHAVIOR OF CRYSTALLINE PHASES CLOSE TO QUASI-CRYSTALS

The crystalline approximant phases alpha-AlMnSi and R-AlCuFe present for alloys of metallic elements anomalous electronic transport properties, with low conductivity values and strong temperature dependences of both the conductivity and the Hall coefficient. In both the alpha- and R-phases, the high field magnetoconductivity can be analysed by quantum interference effects. The transport behaviours are very similar to those of the high structural quality icosahedral phases. Moreover, the R-AlCuFe phase properties are identical to those of the AlCuFe icosahedral phases of the same composition. Surprisingly, the alpha-AlMnSi phase, of a much simpler structure than R-AlCuFe, presents the same anomalous behaviours. Approximants are very different from the icosahedral AlMnSi counterparts which behave like amorphous metals. The results indicate that the relevant length scale for understanding the transport properties is about the size of these crystalline unit cells, i.e. one or two nanometers.