The Effect of Silicon Substitution by Boron for the α-Nb5Si3: INSIGHTS into the Constitutive Properties of Nb5Si2B Through Theory and Experimental Approach

Abstract

We investigated the structural, elastic, vibrational, and electronic properties of the Nb₅Si₂B compound combining density functional theory (DFT) calculations and experimental methods. We compared our results with the parent compound Nb₅Si₃ with two non-equivalent Si sites namely Si(4a) and Si(8h). The analysis of elastic constants and phonon spectra indicate that Nb₅Si₂B is respectively mechanically and dynamically stable. Based on the phonon calculation we evaluate the theoretical constant volume lattice specific heat (C_V) for different site occupancies and compare it with experimental specific heat (C_p) measurements. We found an excellent agreement between theoretical and experimental results for Nb₅Si₂B with the B at the Si(8h) site, which agrees with the calculated formation energy. In addition, we also performed DFT calculations aimed at showing and comparing the total DOS near the Fermi level (E_F) for Nb₅Si₃ and Nb₅Si₂B. The XPS valence band (VB) of the Nb₅Si₂B is largely dominated by two characteristic peaks at − 8.7 and − 1.7 eV, respectively. Based on DFT calculations, it follows that the main sharp peak at − 1.7 eV comes as a contribution from Nb 4d states, while the smaller and broader one located at − 8.7 eV results mainly from Si 3s states weakly hybridized with Nb 4d states. In this connection, the majority contribution in the binding energy range from − 12 eV to the E_F comes from Nb 4d states, while the contribution from Si and B atoms is very small in this region. The core levels of Nb 3d, Si 2s, 2p, and B 1s were also identified using the XPS technique.