The thermoelectric power of Ca₁xAlx, Ca₆₀Al₄₀y Gay and La₁xAlx metallic glasses

Abstract

The thermopower, S, and normalized resistance, R(T)/R(,o), as a function of temperature of some Ca(,1-x)Al(,x), .20 < x < .45, Ca(,.60)Al(,.40-y)Ga(,y), y = .10 and .20, and La(,1-x)Al(,x), .18 < x < .35 metallic glasses have been measured. It is found that the temperature coefficient of resistivity, (alpha) = (rho)('-1)d(rho)/dT, for all the samples is negative and the thermopower is positive for the Ca(,1-x)Al(,x) and Ca(,.60)Al(,.40-y)Ga(,y) alloys while it is negative for the La(,1-x)Al(,x) alloys. The thermopower and resistivity of the Ca(,.55)Al(,.45), Ca(,.60)Al(,.40) and both Ca-Al-Ga alloys are anomalously high. The value of 502 (mu)(OMEGA)-cm and 32 (eta)V/K('2) for the Ca(,.60)Al(,.20)Ga(,.20) alloy are the largest reported room temperature value of (rho) and S/T, respectively, of any non-magnetic amorphous alloy. The value of S/T for the Ca(,1-x)Al(,x) alloys with x = .30, .33, .40 and .45 increase steadily as the temperature decreases and exhibit a small shoulder like structure at approximately 50 K. Below this temperature S/T increases much more rapidly and reaches a maximum value at very low temperatures. This type of temperature dependence in S/T is also observed in both Ca-Al-Ga alloys with the exception that the shoulder like structure is much less pronounced. The value of S/T for the La(,1-x)Al(,x) alloys remains relatively constant at high temperatures, ((theta)(,D) < T < 300 K). However, below (theta)(,D), the value of S/T exhibits a smooth and rapid increase as the temperature decreases and reaches a maximum value just before the onset of superconductivity. The observed temperature dependence of the thermopower at low temperatures, (T < (theta)(,D)), may be understood in terms of the electron-phonon mass enhancement. Neither the Ziman-Faber diffraction model nor the Mott s-d scattering model are able to explain the magnitude and compositional dependence of the thermopower and resistivity of these three alloy systems.