First-principles study on structural, mechanical, electrical, optical and thermal properties of lithium- and calcium-based catalysts

Abstract

This work presents a systematic first-principles study of the crystal structure, mechanical, electrical, optical, and thermodynamic properties of lithium- and calcium-based catalysts (Li3N, Ca3N2, Li3BN2, and Ca3B2N4) for the production of c-BN. The mechanical findings indicate that Ca3N2 is identified as a ductile material, with a higher B/G (20.04) and Poisson's ratio (0.48). The other three materials are recognized as brittle materials, with B/G less than 1.75 and Poisson ratio less than 1/3. The electrical discoveries show that Li3BN2 has the widest band gap among the four catalyst materials, and the band gap of ternary catalyst materials (Li3BN2 and Ca3B2N4) is larger than that of corresponding binary catalyst materials (Li3N and Ca3N2). The optical results reveal thatLi3N, Ca3N2, Li3BN2,and Ca3B2N4 have sufficient energy to prevent charge carriers from being scattered or captured by material defects. The absorption peaks of Ca-based materials (Ca3N2 and Ca3B2N4) are significantly higher than those of Li-based materials (Li3N and Li3BN2). In this frequency range,the light is the most difficult to pass through in Ca3N2 and the easiest to propagate in Ca3B2N4. The connection between Li3N and Ca3N2 bands is greater, while the Li3BN2 and Ca3B2N4 bands interact rather weakly. The thermodynamic conclusions demonstrate that the thermal stability of the four structures is as follows: Li3N< Ca3N2< Li3BN2< Ca3B2N4. The heat capacities of Li3N, Ca3N2, Li3BN2, and Ca3B2N4 tend to approach 23.74, 52.05, 70.73, and 311.48 J∙mol−1∙K−1, respectively.