The effects of interstitials clustering on the configurational entropy of bcc solid solutions

TL;DR

This paper introduces a new analytical model for calculating the configurational entropy in bcc solid solutions with interstitial clustering, applicable to various interstitial types and validated on Nb-H and Zr-H systems.

Contribution

A simple, parameter-free analytical expression for configurational entropy that accounts for interstitial clustering in bcc solutions is proposed and validated.

Findings

Model explains the entropy behavior in Nb-H with H pairs and double pairs.

Accurately describes the partial entropy in Zr-H with H clustering.

Provides insights into interstitial clustering effects on entropy.

Abstract

This work presents a simple model for describing the interstitials behavior in solid solutions enlarging the current random interstitial atoms paradigm. A general and parameter-free analytical expression to compute the configurational entropy, valid for any tetrahedral or octahedral interstitial solutions and suitable for the treatment of interstitials clustering, is deduced for that purpose. The effect of interstitials clustering on the configurational entropy is shown by applying the methodology to the Nb-H and bcc Zr-H solid solutions. The model for Nb-H presented in this work, based on the existence of H pairs in the \alpha phase and double pairs in the \alpha 'phase, provides the basis to explain the unsolved controversies in this system. The unusual shape of the partial configurational entropy measured in bcc Zr-H can be accurately described if a small amount of H clusters are included in the solution.