First-principles study of phase stability of Gd-doped EuO and EuS

TL;DR

This study uses first-principles calculations to analyze the phase stability and solubility of Gd-doped EuO and EuS, revealing stable disordered solutions and potential stabilization of GdO.

Contribution

It provides the first detailed phase diagrams and solubility estimates for Gd-doped EuO and EuS using advanced computational methods.

Findings

Gd-rich EuO has a wide miscibility gap and ordered compounds on Eu-rich side.

GdS has no stable compounds, unlike EuO.

Gd solubility in EuO and EuS is 10-20% at room temperature, increasing with temperature.

Abstract

Phase diagrams of isoelectronic Eu$_{1-x}$Gd$_x$O and Eu$_{1-x}$Gd$_{x}$S quasi-binary alloy systems are constructed using first-principles calculations combined with the standard cluster expansion approach and Monte-Carlo simulations. The oxide system has a wide miscibility gap on the Gd-rich side but forms ordered compounds on the Eu-rich side, exhibiting a deep asymmetric convex hull in the formation enthalpy diagram. The sulfide system has no stable compounds. The large difference in the formation enthalpies of the oxide and sulfide compounds is due to the contribution of local lattice relaxation, which is sensitive to the anion size. The solubility of Gd in both EuO and EuS is in the range of 10-20% at room temperature and quickly increases at higher temperatures, indicating that highly doped disordered solid solutions can be produced without the precipitation of secondary phases. We also predict that rocksalt GdO can be stabilized under appropriate experimental conditions.