An Investigation of Atomic Short Range Order (SRO) in Binary Ni20Pd80 and Au25Pd75 Alloy

Abstract

The atomic short range order (SRO) parameters (αi) have been investigated in polycrystalline alloys i.e., Ni20Pd80 and Au25Pd75. The Ni20Pd80 alloy was annealed at different temperatures (100 to 600°C) then studied with X-ray diffraction (XRD). The electronic theory of atomic short range order (SRO) was utilized to determine the ordering energies and SRO-parameters (αi) for Ni20Pd80 and Au25Pd75 alloy using the pseudo-potential approximation technique. The obtained experimental results of the atomic SRO-parameters (αi) were compared with theoretical results. The intensity distribution pattern of Ni20Pd80 alloy obtained through XRD depicts a deviation from random structure at different annealing temperatures. We make an analysis using the prior obtained X-ray intensities of Ni20Pd80 and calculated the atomic short range order-function (SROF) g(r) as a function of annealing temperatures. Some of the values of αi calculated by using SROF appear as negative, indicating the existence of SRO in Ni20Pd80 alloy. We have obtained the parameters for second and third nearest neighbors, which turned out to be positive. It was found that this theory predicts the same sign of α1 for selected alloy as observed from the experiment. The results can be further improved by considering the order of perturbation and the atomic size effect for the studied alloys. The α1 were studied in Au25Pd75 alloy using the frame work of the transition metal model pseudo-potential (TMMP). Electronic theory of alloys in the pseudo-potential approximation was employed to calculate the ordering energies and the values of α1. It was found that this theory predicts the same sign of α1 for selected alloys.