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Seminarji / Predavanja

 

10. marec 2010 ob 12:00, Kolarjeva predavalnica
 

Specific electron transport properties of Complex Metallic Alloys versus complexity


Prof. Jean-Marie Dubois

Director, Institut Jean Lamour
, UMR 7198 CNRS Nancy-Universite UPV-Metz, Ecole des Mines, Parc de Saurupt, CS14234, F-54042 Nancy, France

Complex metallic alloys (CMA) are characterized by the formation of large building units, comprising several tens of atoms and which most often exhibit icosahedral point group symmetry. As a result, the crystal unit cell may contain up to thousands of atoms.  In quasicrystalline CMAs, the unit cell is no longer an appropriate frame of reference in 3D space because it is infinitely large. Although formed by metal atoms, the electron transport properties of quasicrystalline CMAS and of their approximants (crystals that resemble them, but with a giant unit cell) are certainly not representative of a metallic alloy anymore. A well-documented example is thermal conductivity, which in Al-Cu-Fe or Al-Pd-Mn quasicrystals, is as low as that of zirconia at room temperature.

The correct interpretation of the underlying mechanisms is related to the breakdown of Bloch's theorem due to the loss of crystal periodicity combined with the shrinkage to the origin in reciprocal space of the Brillouin zone. Furthermore, phason jumps, or atoms that pop from an atomic position to another position at short distance like in a double-well potential, also contribute to reduce the conductivity.

The talk will focus at experimental data and will show how thermal conductivity scales with the complexity of the lattice in a series of Al-based CMAs. Similarly, it will show that the same trend is observed along the formation of d-like states in another series of Al-Mg alloys, made of elements that contain no d-states in their valence band before alloying. As a preliminary step, a definition of complexity in CMAs will be given.

 

comments & suggestions to:  sanja fidler