International Research Journal of Pure and Applied Chemistry

The atomic short range order (SRO) parameters (α_i) 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 (α_i) for Ni₂₀Pd₈₀ and Au₂₅Pd₇₅ alloy using the pseudo-potential approximation technique. The obtained experimental results of the atomic SRO-parameters (α_i) 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 α_i 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.