Raman Spectroscopy Signatures of Boron-Rich Superhard Materials from Density Functional Theory

Abstract

Boron-rich superhard materials have complex structural and chemical variations, making it challenging to determine their atomic structures precisely from experiments. Here, we employ first-principles calculation to examine Raman spectra of four boron-rich icosahedral crystals: boron carbide (B 4 C), boron-rich boron carbide (B 13 C 2 ), boron suboxide (B 6 O), and boron subphosphide (B 12 P 2 ). We find qualitative agreements in Raman peak locations between the calculated Raman spectra and the experimental measurements. Furthermore, vibrations of the icosahedra or chains, occurring in all the spectra, are interpreted by performing vibration mode analyses. Our results indicate that the vibrations of the two-atom chain are responsible for the low-frequency region of B 6 O and B 12 P 2 . In contrast, both low-frequency and high-frequency regions are partially related to the vibration of chain atoms for B 4 C and B 13 C 2 . Besides, the icosahedral vibration modes are attributed to the high-frequency region of all these four crystals. More importantly, the peak positions of Raman spectra can be used to identify the various icosahedral structure with different B/C ratios and various chain structures, making Raman spectroscopy an important tool to monitor the processing of newly developed icosahedral materials with enhanced physical properties. This study not only provides a deeper understanding of the atomic structures of boron-rich superhard materials from the perspective of Raman spectroscopy but also helps to interpret the experimental Raman spectra.

Combustion synthesized boron carbide powders by different organic carbon sources and microwave absorbing properties

“…29 The red shift of the Raman peak is due to the substitution of boron and carbon atoms on the icosahedron and atomic chain, which is the main reason why boron carbide has a variety of isomers. 36 This is consistent with the XRD results. In addition, the characteristic double peaks with gentle peak shapes at 1350 cm −1 (D peak) and 1580 cm −1 (G peak) were obvious, indicating an increase in the disorder of the residual carbon structure.…”

“…Among them, the two characteristic peaks at 475 and 530 cm −1 in the low‐frequency region are the vibrational modes of the C–B–C chain, and the two shoulder peaks at 708/813 and 990/1075 cm −1 in the high‐frequency region are the characteristic vibration of the B 11 C icosahedron 29 . The red shift of the Raman peak is due to the substitution of boron and carbon atoms on the icosahedron and atomic chain, which is the main reason why boron carbide has a variety of isomers 36 . This is consistent with the XRD results.…”