Insight into Physical and Thermodynamic Properties of X3Ir (X = Ti, V, Cr, Nb and Mo) Compounds Influenced by Refractory Elements: A First-Principles Calculation

Dong Chen,Cunjuan Xia,Yi Wu,Jiwei Geng,Mingliang Wang

doi:10.3390/cryst9020104

Abstract

The effects of refractory metals on physical and thermodynamic properties of X3Ir (X = Ti, V, Cr, Nb and Mo) compounds were investigated using local density approximation (LDA) and generalized gradient approximation (GGA) methods within the first-principles calculations based on density functional theory. The optimized lattice parameters were both in good compliance with the experimental parameters. The GGA method could achieve an improved structural optimization compared to the LDA method, and thus was utilized to predict the elastic, thermodynamic and electronic properties of X3Ir (X = Ti, V, Cr, Nb and Mo) compounds. The calculated mechanical properties (i.e., elastic constants, elastic moduli and elastic anisotropic behaviors) were rationalized and discussed in these intermetallics. For instance, the derived bulk moduli exhibited the sequence of Ti3Ir < Nb3Ir < V3Ir < Cr3Ir < Mo3Ir. This behavior was discussed in terms of the volume of unit cell and electron density. Furthermore, Debye temperatures were derived and were found to show good consistency with the experimental values, indicating the precision of our calculations. Finally, the electronic structures were analyzed to explain the ductile essences in the iridium compounds.

Highlights

Ir-based superalloys have received intensive interest in the last decades due to their high melting temperature as well as their improved strength, oxidation resistance and corrosion resistance at higher temperatures [1,2,3,4,5]
The first-principles calculations were performed using the CASTEP code, which is based on the pseudopotential plane-wave within density functional theory [20,21]
Using the ultrasoft pseudopotential [22] to model the ion-electron exchange-correlation, both the generalized gradient approximation (GGA) with the function proposed by Perdew, Burke and Ernzer (PBE) [23,24] and the local density approximation (LDA) with Ceperley–Alder form [25] were used

Summary

Introduction

Ir-based superalloys have received intensive interest in the last decades due to their high melting temperature as well as their improved strength, oxidation resistance and corrosion resistance at higher temperatures [1,2,3,4,5]. These intermetallics can be deemed a suitable choice for high-temperature applications. Terada et al [6] conducted measurements on thermal properties (i.e., thermal conductivity and thermal expansion) from 300 to 1100 K, and found that the L12 Ir3 X (X = Ti, Zr, Hf, Nb and Ta) compounds were characterized by a larger thermal conductivity and a smaller thermal expansion. Liu et al [8] studied the elastic and thermodynamic properties of Crystals 2019, 9, 104; doi:10.3390/cryst9020104 www.mdpi.com/journal/crystals

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Results

Conclusion