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 (Li _3 N, Ca _3 N _2 , Li _3 BN _2 , and Ca _3 B _2 N _4 ) for the production of cubic boron nitride. The mechanical findings indicate that Ca _3 N _2 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 Li _3 BN _2 has the widest band gap among the four catalyst materials, and the band gap of ternary catalyst materials (Li _3 BN _2 and Ca _3 B _2 N _4 ) is larger than that of corresponding binary catalyst materials (Li _3 N and Ca _3 N _2 ). The optical results reveal that Li _3 N, Ca _3 N _2 , Li _3 BN _2 , and Ca _3 B _2 N _4 have sufficient energy to prevent charge carriers from being scattered or captured by material defects. The absorption peaks of Ca-based materials (Ca _3 N _2 and Ca _3 B _2 N _4 ) are significantly higher than those of Li-based materials (Li _3 N and Li _3 BN _2 ). In this frequency range, the light is the most difficult to pass through in Ca _3 N _2 and the easiest to propagate in Ca _3 B _2 N _4 . The connection between Li _3 N and Ca _3 N _2 bands is greater, while the Li _3 BN _2 and Ca _3 B _2 N _4 bands interact rather weakly. The thermodynamic conclusions demonstrate that the thermal stability of the four structures is as follows: Li _3 N< Ca _3 N _2 < Li _3 BN _2 < Ca _3 B _2 N _4 . The heat capacities of Li _3 N, Ca _3 N _2 , Li _3 BN _2 , and Ca _3 B _2 N _4 tend to approach _2 3.74, 52.05, 70.73, and 311.48 J·mol ^−1 ·K ^−1 , respectively.

Keywords

• mechanical properties
• electrical properties
• optical properties
• thermodynamic properties
• catalysts