Interionic Pair Potential, hard sphere diameter and entropy of mixing of NaCd compound forming binary molten alloys under the framework of Pseudopotential theory

Abstract

The observed asymmetric behaviour of mixing of  NaCd liquid alloys around equiatomic composition with smaller negative values for free energy of mixing at compound forming concentration, i.e. G_M^XS = -4.9KJ at C_cd =0.66 has  aroused our interest to undertake a theoretical investigation of this system.

A simple statistical mechanical theory based on compound formation model has been used to investigate the energetics of formation of intermetallic compound Cd₂Na in the melt through the study of entropy of mixing.

Besides, the interionic interactions between component atoms Na and Cd of the alloys have been understood through the study of interionic pair potential Ñ„_ij(r), calculated from pseudopotential theory in the light of CF model.

Our study of Ñ„_ij(r) suggest that the effective interaction between Na-Na atoms decreases on alloying with Cd atom, being minimum for compound forming alloy( Cd _0.66 Na _0.34 ).The nearest neighbor distance between Na-Na atoms does not alter on alloying. Like wise Na-Na,  effective interaction between  Cd-Cd atom decreases from pure state to NaCd alloys, being smaller at compound forming  concentration Cd _0.66 Na _0.34.The computed values of S_M from pseudopotential theory are positive at all concentrations, but the agreement between theory and experimental is not satisfactory. This might be happening due to parameterisation of σ₃ and Ψcompound.