Negative-temperature coefficients of electrical resistivity in amorphous La-based alloys

Abstract

A negative-temperature coefficient ($\ensuremath{\alpha}=\frac{{\ensuremath{\rho}}^{\ensuremath{-}1}d\ensuremath{\rho}}{\mathrm{dT}}$) of electrical resistivity, $\ensuremath{\rho}(T)$, has been observed in many amorphous and disordered metallic conductors. The origin of this anomalous temperature dependence of resistivity is still unclear. To explain the negative-$\ensuremath{\alpha}$ anomaly, there are two theoretical approaches (i.e., the Ziman-type theory and the structural Kondo model) currently discussed in the literature. In an attempt to distinguish between these two approaches the resistivity of several liquid-quenched amorphous La-based alloy systems containing Al, Au, Ga, or Ge, has been analyzed as a function of composition and temperature. It is concluded that the resistivity data are inconsistent with the Ziman-type theory and are in favor of the structural Kondo-type model. This conclusion is based on the fact that (1) resistivity varies as $\ensuremath{-}\mathrm{ln}T$ ($T\ensuremath{\gtrsim}100$ K) in alloys with negative $\ensuremath{\alpha}$, and (2) the occurrence of negative $\ensuremath{\alpha}$ is independent of the valence of the La-based alloys.