Thermodynamic properties and local structures of non-stoichiometry. Galvanic cell study of fused InxI1–x mixtures

Abstract

Thermodynamic studies of fused non-stoichiometric In_xI_1–x mixtures have been carried out by determining the partial thermodynamic parameters of the In component using a galvanic cell method. The integral entropy and enthalpy of mixing were computed with the mixtures as fused In(x_r)+ InI₃(1 –x_r). As a further effort to determine the ionic arrangements the long-wavelength limit of the concentration correlation function, S_cc(0), was calculated and developed to examine the crude short range ordering, ΔN_α, and the role of charge transfer, Δe_In. Large deviations were seen in all the thermodynamic parameters and in the above-mentioned structure parameters for these molten metal + non-metal mixtures, in particular near the stoichiometric composition InI₂(x= 0.333 or x_r= 0.333). These marked composition trends have been interpreted as a consequence of there being two different electronic states for In (i.e., InI^–₄ and In⁺) or of the covalent and ionic bondings between unlike nearest neighbours in the vicinity of InI₂.