Ab initio aided design of novel quaternary, quinary and senary high-entropy borocarbides

Daniel Hedman,Ana C Feltrin,Farid Akhtar,Yoshiyuki Miyamoto

doi:10.1007/s10853-021-06600-y

Abstract

High-entropy materials have attracted considerable interest due to their unique, improved properties and large configurational entropy. Out of these, high-entropy ceramics (HECs) are of particular interest since the independent solubility of cations and anions results in increased configurational entropy. However, most HEC research considers only a single element occupying the anion sublattice, which limits the maximum attainable configurational entropy. Here, we expand our previous work on high-entropy borocarbides where both boron and carbon occupy the anion sublattice. By applying an ab initio based screening procedure, we identify six elements Li, Ti, V, Zr, Nb and Hf suitable for forming high-entropy borocarbides. With these elements, we propose six novel HEC compositions, and by computing their entropy forming ability, we identify that three are likely to form single-phase during synthesis. Material properties and lattice distortions for all proposed compositions are studied using density functional theory calculations with special quasirandom structures. The directional lattice distortions, a concept we introduce in this work, show that lattice distortions have an elemental and directional preference for certain HEC compositions. We also show that the novel inclusion of Li improves the mechanical properties of the proposed HECs, the details of which are studied using the electron localization function.

Highlights

High-entropy ceramics (HECs) are synthesized from a mixture of four or more multicomponent ceramic compounds following the concept of configurational entropy stabilization of a single-phase [1, 2]
The entropy forming ability (EFA) descriptor is obtained via ab initio density functional theory (DFT) calculations, and was used by both Sarker et al [9] and Harrington et al [17] to explore the experimental synthesizability of many different quinary high-entropy carbides
We find six candidate elements Li, Ti, V, Zr, Nb and Hf from which we propose six novel high-entropy ceramic (HEC) compositions

Summary

Introduction

High-entropy ceramics (HECs) are synthesized from a mixture of four or more multicomponent ceramic compounds following the concept of configurational entropy stabilization of a single-phase [1, 2]. The crystal structure of HECs consists of a cation sublattice and anion sublattice [3], which offers independent solubility of cations and anions in one crystal structure, enhancing the configurational entropy [4]. The first reported HECs were high-entropy nitrides [5] and high-entropy oxides [6], followed by highentropy borides [7] and high-entropy carbides [8, 9]. Computational studies have contributed toward the discovery and understanding of HECs through the screening of promising compositions and prediction of their properties, such as the development of the entropy forming ability (EFA) descriptor by Sarker et al which can be used to predict whether a high-entropy composition is likely to form singlephase during synthesis [9]. The EFA descriptor is obtained via ab initio density functional theory (DFT) calculations, and was used by both Sarker et al [9] and Harrington et al [17] to explore the experimental synthesizability of many different quinary high-entropy carbides

Methods

Results

Conclusion