A density functional theory approach to the effects of C and N substitution at the B-site of the first boride MAX phase Nb2SB

Abstract

MAX phases have diverse physical properties and as such are an important research field linked to numerous applications. The recent addition of boride member to the MAX family has further extended the physical properties and diversity of these compounds. In this study, the structural, electronic, mechanical, thermal and optical properties were investigated using the density functional theory (DFT) for Nb2SB. The effects of C and N substitution at the B-site of Nb2SB are also investigated. To do so the conventional carbide and nitride counterparts of Nb2SB have also been calculated. In most cases, the first boride MAX phase Nb2SB is mechanically stronger than its carbide and nitride counterparts. Its elastic constants C11 and C44, elastic moduli G and E, Vickers hardness HV, Debye temperature θD, lattice thermal conductivity κph, minimum thermal conductivity κmin, and melting temperature Tm are higher than those of Nb2SC and Nb2SN. Nb2SB is brittle in nature, whereas Nb2SC and Nb2SN are ductile. Non-central forces are dominant in Nb2SB while the central forces are dominant in Nb2SC and Nb2SN. Nb2SB is more covalent and more resistant to shear deformation than its carbide and nitride counterparts. Elastically and optically, Nb2SB is less anisotropic than its carbide and nitride counterparts. Data availabilityData will be made available upon reasonable request.