Temperature dependence of the structure factor in Nb-Ni glasses

Abstract

Using the results of x-ray scattering experiments, the structure factor $S(k)$, the radial distribution function, and the coordination number have been determined at room temperature for two Nb-Ni glass samples (of composition ${\mathrm{Nb}}_{0.4}$${\mathrm{Ni}}_{0.6}$ and ${\mathrm{Nb}}_{0.5}$${\mathrm{Ni}}_{0.5}$). Furthermore, the height of the first peak in the structure factor, $S({k}_{p})$, has been measured as a function of temperature for these two samples in the range 4-675 K. $S({k}_{p})$ remains approximately constant from 4 to \ensuremath{\sim}100 K, after which it decreases linearly with increasing temperature until the glass crystallizes at \ensuremath{\sim}675 K. This behavior is in excellent agreement with a recent calculation which expresses the temperature dependence of $S(k)$ of an amorphous metal in terms of the Debye-Waller factor. According to the Ziman theory for the resistivity of amorphous metals, a decrease of $S({k}_{p})$ with increasing temperature may lead to a negative temperature coefficient of resistivity as has been observed in these glasses. The observed change of $S({k}_{p})$ is large enough to account for the observed change in resistivity at room temperature and above. Possible reasons for the discrepancy between the Ziman theory and the structure-factor data below room temperature are discussed.