Structural, electronic properties and boron stability of (001) surface of Nb₅Si₃ intermetallic by first-principles calculations

The structural, electronic and surface properties of (001) surface with four different terminations of Nb₅Si₃ are discussed by using the first-principles calculations in this research. Firstly, we discuss the formation enthalpy and density of states of bulk Nb₅Si₃, finding that the calculated results are consistent with the previous experimental and calculated data. It can be interpreted as that the calculated method used is credible. The relaxed degree is explicitly described by the relaxed parameters (Δz, δz, d_i,i+1 and r_i) of (001) surface. Density of states shows that the outermost layer states are the major ingredient for surfaces and the surface states arise after the formation of surfaces. The lowest surface energy reflects that (001)-Si surface is the most stable surface. The segregation energy, interlayer spacing and density of states are calculated to discuss the boron stability in Nb2-and NbSi-terminations surfaces. According to the segregation energy, we know that boron is more stable at surface than Sub2 and the segregation energy of inner layer is positive, indicating that we can adopt some methods like heating to drive boron segregating to surface, which can form the protective oxide layers to ameliorate the oxidation resistance of surface. The intensive bonding interactions between B and its contiguous atoms origin from the investigation of interlayer relaxations. After B substitutions, the density of states has the changes that appear at its substitutional layer and the metallic properties are decreased in the two terminations surfaces. Oxygen adsorption further verify that alloying B can promote the oxidation resistance of Nb₅Si₃.