Fermi-Surface-Brillouin-Zone Interaction in Simple Cubic Te-Au Alloys

The lattice spacing, superconducting transition temperature, and thermoelectric power of simple cubic Te-Au alloys (60-85 at.% Te) obtained by rapid quenching from the liquid state have been measured. The lattice parameter increases with increasing Te content. A change in slope in the lattice-parameter-versus-composition curve is observed at 68 at.% Te. A broad maximum (at 70 at.% Te) and a broad minimum (at 80 at.% Te) are observed in the variation of the superconducting transition temperature with concentration. The thermoelectric power is measured as a function of concentration and of temperature. The thermoelectric power at 290°K is negative in alloys containing up to 76 at.% Te and positive above this concentration. The thermoelectric-power anomalies at 70 and 80 at.% Te correspond to those in the plot of superconducting transition temperature versus composition. As a function of temperature, the thermoelectric power of all the simple cubic alloys studied is linear from ∼140 to 300°K. The observed anomalies in the variation of the lattice parameter, thermoelectric power, and superconducting transition temperature can be qualitatively interpreted in terms of a Fermi-surface-Brillouin-zone interaction. The main conclusions can be stated as follows: (1) The thermoelectric-power data can be analyzed to yield information about the Fermi-surface-Brillouin-zone interaction. (2) The conduction-electron-per-atom ratio increases with increasing tellurium content. Consequently, the Fermi energy of the simple cubic alloys increases as gold atoms are replaced by tellurium atoms. (3) The Fermi surface makes an initial contact with the third Brillouin zone at around 70 at.% Te. (4) The second and third bands overlap at about 80 at.% Te. The second Brillouin zone is not completely filled at 85 at.% Te. (5) The experimental results seem to suggest that the effect of Fermi-surface-Brillouin-zone interaction on the variation of the lattice parameter with concentration is a general phenomenon, in the sense that it can occur regardless of the type of crystal structure. (6) The results on the superconducting transition temperature as a function of concentration seem to be consistent with the thermoelectric-power and lattice-parameter results.