First Principles Density Functional Theory Prediction of the Crystal Structure and the Elastic Properties of Mo2ZrB2 and Mo2HfB2

Rachid Stefan Touzani,Manja Krüger

doi:10.3390/cryst10100865

Rachid Stefan Touzani, Manja Krüger

Open Access

https://doi.org/10.3390/cryst10100865

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Journal: Crystals	Publication Date: Sep 24, 2020
Citations: 4	License type: CC BY 4.0

Affiliation: Otto-von-Guericke University Magdeburg

Abstract

The Molybdenum rich ternary alloys Mo-M-B (M = Zr, Hf) contain, next to the Mo solid solution (bcc Mo with small amounts of Zr or Hf as substitutional atoms), the binary borides Mo2B, MB and MB2. Recently, it was found that there is also ternary Mo2MB2, but the crystal structure and further properties are currently unknown. Density functional theory (DFT) calculations were used not only to predict the crystal structure of the Mo2MB2 phases, but also to estimate the isotropic and anisotropic elastic properties like bulk, shear and Young’s modulus, as well as the Vickers hardness of these new borides. Several known crystal structures that fulfill the criterion of the chemical composition were investigated, and the AlMn2B2 type structure seems to be the most stable crystal structure for Mo2HfB2 and Mo2ZrB2 as there are no signs of electronic or dynamic instability. Regarding the elastic properties, it was found that Mo2HfB2 shows higher elastic moduli and is less elastically anisotropic than Mo2ZrB2.

Highlights

There is a significant demand for new high-performance materials for technically challenging applications, e.g., in the metal processing industry, or in the energy generation and the aviation sectors.It is well-accepted that the materials capability affects the performance of machines, like turbines [1].State-of-the-art materials for heavily stressed structural components are single-crystalline nickel-based superalloys
Based on the measured chemical composition 2-1-2 for Mo, M (M = Zr, Hf) and B, respectively, for the new compounds [14,15], we took 50 crystal structures of already known 2-1-2 and 3-2 intermetallics that fulfill the above-mentioned criterion of composition. Of those 50 types of crystal structures, the nine that showed the lowest total energy were those of the AlMn2 B2 -type [19], the Mo2 FeB2 -type [20], the Nb2 OsB2 -type [21], the U2 Pt2 Sn-type [22], the CeAl2 Ga2 -type, the β-Cr2 IrB2 -type [24], the Mo2 IrB2 -type [25], the HoNi2 B2 -type [26] and the W2 CoB2 -type [27]
Exchange and correlation in this density functional theory (DFT)-based method were treated with the generalized gradient approximation (GGA) functional as parameters by Perdew, Burke and Ernzerhof (PBE-GGA) [36]

Summary

Introduction

There is a significant demand for new high-performance materials for technically challenging applications, e.g., in the metal processing industry, or in the energy generation and the aviation sectors.It is well-accepted that the materials capability affects the performance of machines, like turbines [1].State-of-the-art materials for heavily stressed structural components are single-crystalline nickel-based superalloys. There is a significant demand for new high-performance materials for technically challenging applications, e.g., in the metal processing industry, or in the energy generation and the aviation sectors. The most challenging goal is to develop new high-temperature materials that provide balanced properties in a wide temperature range, i.e., sufficient fracture toughness at low and ambient temperatures, as well as creep strength and appropriate oxidation resistance at ultra-high temperatures. This target could be met by tailored refractory metal alloys, e.g., those based on molybdenum [2,3,4,5]

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