Effects of short-range order on electronic properties of Zr-Ni glasses as seen from low-temperature specific heat

Measurements of the low-temperature specific heat $C_p$ of liquid-quenched Zr-Ni glasses for a large number of compositions in the range from 55 to 74 at.% Zr revealed an unusual composition dependence of the density of states at the Fermi level, $N\left(E_F\right)$. Furthermore, for some compositions the variation of $C_p$ near the superconducting transition temperature $T_c$ indicated the presence of two superconducting phases, i.e., two superconducting transitions were detected. Comparison of the individual $T_c$'s in phase-separated samples to the composition dependence of $T_c$ for all of the samples suggests that amorphous phases with compositions near 60 and 66.7 at.% Zr occur. We discuss these results in terms of an "association model" for liquid alloys (due to Sommer), in which associations of unlike atoms with definite stoichiometries are assumed to exist in equilibrium with unassociated atoms. We conclude that in the composition range studied, associate clusters with the compositions ${\mathrm{Zr}}_3$ ${\mathrm{Ni}}_2$ and ${\mathrm{Zr}}_2$Ni occur. In only a few cases are the clusters sufficiently large, compared with the superconducting coherence length, for separate superconducting transitions to be observed. The variation of $N\left(E_F\right)$ with composition is discussed, as well as the effects of this chemical short-range ordering on the crystallization behavior and glass-forming tendency.