Comparison of the Physical Properties and Electronic Structure of Nb2B3 and Ta2B3

Based on the first-principles method, the effects of pressure and temperature on the physical properties of Nb2B3 and Ta2B3 were discussed. The approximate linear increase in B, G, and E with pressure was observed for Nb2B3 and Ta2B3 with a minor difference for bulk modulus and similar values for shear and Young’s modulus. Nb2B3 shows higher Vickers hardness and similar fracture toughness as compared with Ta2B3. An abnormal phenomenon of the simultaneous increase in hardness and B/G (σ) with the increased pressure was observed. The strong anisotropies of bulk, Young’s, and shear modulus were observed, and the differences of anisotropy between Nb2B3 and Ta2B3 increased with pressure. At low temperatures, the α of Nb2B3 is smaller than that of Ta2B3, but is larger than that of Ta2B3 at high temperatures. The Θ of Nb2B3 are larger than those of Ta2B3 under the same conditions. The combination of relatively high Vickers hardness and fracture toughness is determined by the metallic bond and covalent bond. With the increased pressure, Nb2B3 possesses the greater strength of B–B bonds than Ta2B3, which leads to its high hardness and Debye temperature.