Chemical short-range order in dense random-packed models

Abstract

We used a dense random-packed model of an amorphous alloy to calculate the partial correlation functions, which in turn were used to derive the radial distribution functions, the Bathia-Thorton number-concentration fluctuations and the partial interference functions. We applied the model to amorphous Ni 35Zr 65 using atomic radii of 1.10 and 1.58 Å for nickel and zirconium respectively. We included chemical short-range order (CSRO) in the model by permuting nickel-zirconium nearest-neighbor atom pairs in response to a decrease in the enthalpy of the alloy. The permutations decreased the Warren-Cowley order parameter from zero to −0.038, a value in good agreement with the measured value of −0.040. The increase in CSRO is accompanied by the appearance of a peak in the partial interference function I Ni- Ni ( K) at K = 1.9 A ̊ −1 . The peak is similar in form to the socalled prepeak commonly observed in rapidly quenched binary amorphous alloys containing nickel and is located at the same value of K. We tentatively atribute the increase in CSRO and the appearance of the prepeak in I Ni- Ni ( K) to the formation of double tetrahedra with three zirconium atoms at the base and two nickel atoms at the apices.