Experimental test of the extended Ziman theory, using free electron-like Ag-Cu based amorphous alloys

Abstract

Electron transport properties have been studied in a number of Hume-Rothery type amorphous thin film alloys prepared by the vapour quenching method. Alloy systems employed were the ternary systems based on the Ag-Cu binary eutectic. Amorphous phases stable at room temperature were found in the following composition ranges: 0<or=x<or=0.8 in (Ag0.5Cu0.5)1-xMgx, 0<or=x<or=0.7 in (Ag0.5Cu0.5)1-xAlx and 0<or=x<or=1.0 in (Ag0.5Cu0.5)1-xGex. In all amorphous alloys except those with Ge content higher than x=0.3, the Fermi diameter 2kF, deduced from the Hall coefficient, agrees well with the corresponding free electron value. The formation of a stable amorphous phase in a wide composition range with an added third element, having a valence higher than one, allowed a wide range of well-defined 2kF values to be mapped out and correlated with the composition dependence of rho 300K and the TCR. This provided a unique opportunity for testing the validity of the Ziman theory for the electron transport property of an amorphous alloy near room temperature. It was confirmed that the 2kF/Kp ratio indeed closely controls the behaviour of the TCR, and that the TCR changes its sign at 0.98, in good agreement with the Ziman theory. However, it was also revealed that a negative TCR continues to exist even when the 2kF/Kp ratio exceeds 1.15.