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Title: Evaluation of partial and total structure factors, Bhatia-Thornton correlation functions, compressibility and diffusion coefficient of Pb-Pd alloy at different compositions and temperatures
Authors: Bandyopadhyay, Sumita
Venkatesh, R
Gopala Rao, R V
Issue Date: Jan-2002
Publisher: NISCAIR-CSIR, India
Abstract: The partial and total structure factors of Pd-Pb alloy have been computed using Lebowitz solution of hard spheres with a square well attractive tail. The calculated values of the total structure factors and also that of the reduced radial distribution function are in excellent agreement with experiment. It is found that the partial structure factors show peculiarities due to the formation of a compound Pb2Pd as reported by Christian et al.[J Noncryst Solids, 156( 1993)38]. Bhatia-Thornton correlation functions are also calculated, namely, SNN(k), which show sirong correlation in k-space while Scc(k) and SNC(k) do not show such correlation. The partial and total radial distribution functions (RDF) are also calculated from which first coordination numbers are obtained. The RDFs show for all compositions the first peaks at 3.35Ǻ. Exactly the same value has been obtained by Christian et al. This value is in no way nearer to the first nearest neighbour distances in pure Pb or Pd. Thus, the small value of 3.35Ǻ, which corresponds to the first peak position, has been attributed to the formation of a compound Pb2Pd, which in crystalline form shows exactly the same distance between unlike neighbouring atoms. The values of compressibility have also been calculated, which show a bigger value of 41 .6 × 10-12 cm2/dyne at 60 atomic percent of Pb. This also indicates the formation of a compound. The diffusion coefficients have been calculated through Helfand 's prescription. No observable sudden changes are seen in the case of diffusion coefficient. As suggested by Christian et al., the authors also calculated the total sum of the partial structure factor SS(k), namely that of SPb-Pb(k) and SPb-Pd (k) and a strong right hand shoulder at 60 atomic percent of Pb has been found and this perhaps is a characteristic of compound formation and the shoulder is obtained at 2.8Ǻ while in Pb2Pd an exact distance is found in its crystalline form between unlike atoms. It may be pointed out Pd-Pb distance in amorphous Pb2Pd compound is exactly 2.83Ǻ while the present shoulder is obtained at 2.8Ǻ. Hence it is concluded that Lebowitz solution with a square well attractive tail reproduced several characteristics shown in the experiment and also clearly indicate the formation of a compound.
Page(s): 32-41
ISSN: 0975-1041 (Online); 0019-5596 (Print)
Appears in Collections:IJPAP Vol.40(01) [January 2002]

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