Settling the matter of the role of vibrations in the stability of high-entropy carbides

Marco Esters,David Hicks,Stefano Curtarolo,Corey Oses,Michael J Mehl,Cormac Toher,Donald W Brenner,Michal Jahnátek,Jon-Paul Maria,Mohammad Delower Hossain

doi:10.1038/s41467-021-25979-5

Abstract

High-entropy ceramics are attracting significant interest due to their exceptional chemical stability and physical properties. While configurational entropy descriptors have been successfully implemented to predict their formation and even to discover new materials, the contribution of vibrations to their stability has been contentious. This work unravels the issue by computationally integrating disorder parameterization, phonon modeling, and thermodynamic characterization. Three recently synthesized carbides are used as a testbed: (HfNbTaTiV)C, (HfNbTaTiW)C, and (HfNbTaTiZr)C. It is found that vibrational contributions should not be neglected when precursors or decomposition products have different nearest-neighbor environments from the high-entropy carbide.

Highlights

High-entropy ceramics are attracting significant interest due to their exceptional chemical stability and physical properties
Our findings reveal that: (1) vibrations have a measurable effect on the transition temperature of high-entropy carbides (HECs)-W, and should not be neglected, but have only a small effect on HEC-V and HEC-Zr— we attribute this to the different nearest-neighbor environments in precursors and decomposition products from the high-entropy carbide; (2) the carbide sublattice distorts to accommodate the different metal cations to maximize entropy gains and minimize enthalpic penalties
The decoration breaks the symmetry of the parent structure, causing the lattice of the derivative structure to deviate from the parent upon relaxation

Summary

Introduction

High-entropy ceramics are attracting significant interest due to their exceptional chemical stability and physical properties. 1234567890():,; High-entropy materials are single-phase multi-element systems with large entropy contributions, structural longrange order, and chemical disorder. They have attracted substantial interest in recent years due to their remarkable physical properties and chemical stability[1,2,3,4,5,6]. The starting disordered configurations have commonly been chosen among Special Quasi-random Structures[36] In these structures, the occupation correlations are optimized to resemble ideal disorder: the sampled structures aim to represent snapshots of an infinite-temperature solid solution. The POCC energy spectrum can generate synthesizability descriptors, such as the entropy-forming ability (EFA) The latter was successfully used in 2018 to discover several novel five-metal high-entropy carbides (HECs) from binary precursors[9]

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Results

Conclusion