Effect of disorder on thermodynamic instability of binary rare-earth - nickel - palladium compounds

The investigation of the intermetallic compounds, in particular those formed by the rare earth (R) elements, covers an important area of scientific research, with emphasis on the identification of new phases and their potential use in technological applications. We investigated the thermodynamic and electronic origins of phase instability in SmX₂ and Sm₁₀X₂₁ (X=Ni, Pd) based rare-earth compounds using machine-learning trained analytical descriptor and first-principles density-functional theory. The convex hull construction illustrates why SmPd₂ compound is unstable in the Sm-Pd binary system despite having more negative formation energy than experimentally observed SmNi₂. The instability of disordered Sm(Ni_xPd_1-x)₂ solid solution in MgCu₂ Laves phase is triggered by Pd alloying that reduces the local charge correlation by charge screening effect, which also reduces the underlying Sm-Pd and Ni-Pd hybridization. This work emphasizes both the usefulness and limitations of machine-learned analytical descriptors for quick thermodynamic assessment of phase stabilities, while emphasizing the utility of advanced ab-initio methods for providing key quantum mechanical understanding of structural, thermodynamic, and electronic properties. Specifically, our study highlights peculiar features in band-structure responsible for thermodynamic instability, which can be useful to understand other chemically complex rare-earth compounds.