Entropy terms in statistical thermodynamic analysis formula for non-stoichiometric interstitial compounds

• Autor(a) principal: Shohoji, Nobumitsu
• Data de Publicação: 2019
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10400.9/3190
• topic: Statistical thermodynamics; Non-stoichiometry; Interstitial compound; Entropy terms

ABSTRACT: A series of statistical thermodynamic analyses were made since 1974 for different types of non-stoichiometric interstitial compounds MXx under simplifying a priori assumption of constant interaction energy E(X-X) between nearest neighbour interstitial atoms X within a homogeneity composition range of MXx at arbitrary temperature T [K]. Mode of distribution of X atoms in interstitial sites in MXx lattice is represented by number θ of available interstitial sites for occupation by X atoms per M atom and the value of θ is determined to fulfil the a priori assumption. Mode of atomic configuration would yield major contribution to entropy term ∆S that appears in conventional thermodynamic expression of Gibbs free energy of formation, ∆G, in form of T∆S. In the statistical thermodynamic formulation, contribution of tightly bound electron appearing in form of RT ln fX where fX refers to atomic partition function of X atom in the MXx lattice and R the universal gas constant. Judging from this mathematical form of the term, R ln fX is considered to represent entropic contribution from tightly bound electron to X atom in MXx lattice. In the published series of works on statistical thermodynamic analysis for non-stoichiometric interstitial compounds, calculated values for R ln fX were reported but they were not reviewed with serious attention because R ln fX was considered merely as a secondary factor compared to principal factor E(X-M) referring to interaction energy between X and M in MXx lattice that represents enthalpy ∆H in conventional thermodynamic term. In this review article, consideration is given exclusively to the factor R ln fX evaluated in statistical thermodynamic approach to non-stoichiometric interstitial compounds.