Electronic Properties of Ordered Quasicrystals and Related Phases
An extensive, systematic study of the electronic properties of the well-ordered icosahedral (i-) phases and related crystalline and amorphous phases is presented. Barely metallic behavior is observed in the ordered i-crystals, including high resistivities with large temperature coefficients, low electronic densities of states at the Fermi energy, large values of the low-temperature Hall coefficients, and unusual temperature dependences of the Hall coefficients and the thermoelectric powers. In addition, rapid variations of these properties with small changes in composition are observed. Similar behavior is seen in crystalline approximant structures, which are close crystalline analogues of the i-phase. With increasing structural disorder in disordered i-phases and in the totally disordered amorphous (a-) phases, the familiar metallic-glass-like electronic properties are restored. This striking electronic behavior is shown to be due to band structure effects. The high resistivities, low densities of states, and low carrier densities are shown to be due to the structural scattering mechanism of the Fermi-surface-Jones-zone interaction, which is enhanced due to the high degree of structural ordering and, in the i-phases, due to the icosahedral symmetry. The unusual temperature dependences of the Hall coefficients and thermoelectric powers, as well as the rapid variation of the electronic properties with small changes in composition, support the existence of a rapidly varying density of states on a fine energy scale, on the order of 26 meV. The existence of these band structure effects is further supported by the effects of structural disorder on the electronic properties, with disorder restoring the free-electron metallic-glass -like electronic properties. The temperature dependence of the conductivity at high temperatures displays novel concave upward curvature in a wide variety of icosahedral, amorphous, and crystalline phases which have high resistivity values. Although the existing theory of quantum interaction effects successfully describes the low-temperature conductivity and magnetoconductivity, differences between the theoretical predictions and the data at high temperatures are substantial. These results document previously unaddressed electronic behavior in alloys which are in the barely metallic regime.
- Pub Date:
- ICOSAHEDRAL PHASES;
- Physics: Condensed Matter