Raman spectroscopy of pressure-induced amorphous boron carbide

Abstract

We report low- and high-temperature Raman spectroscopy of pressure-induced amorphous boron carbide (a-B4C). Coarsening of carbon clusters in a-B4C was characterized during heating, whereas unusual temperature coefficients of a-B4C Raman peak shifts were observed during cooling. These results experimentally evidence that the amorphization of B4C is associated with the destruction of the C–B–C chains and a-B4C is composed of sp2 carbon aromatic rings and boron clusters. This disordered structure with relatively weak carbon sp2 bonds is believed to be responsible for the loss of B4C shear strength at high pressures.

Atomic structure of amorphous shear bands in boron carbide

“…2b). These characteristic Raman bands indicate the formation of amorphous B 4 C caused by the indentation, in agreement with previous observations of amorphous B 4 C in single and polycrystalline B 4 C ceramics 14,16,17,19 . ABF-STEM of amorphous shear bands.…”

“…Raman spectroscopy of amorphous B 4 C. In this study, the amorphous B 4 C was introduced by a nanoindentation experiment 14,16,17,19 . Figure 2 shows the representative Raman spectra acquired from the pristine and residual indented regions of B 4 C. The spectrum of the pristine B 4 C displays characteristic Raman peaks at 270, 320, 481, 531, 728, 830, 1,000 and 1,088 cm À 1 assigned to crystalline B 4 C (refs 24,25), A weak band at 1,580 cm À 1 has been attributed to the presence of a small fraction of graphitic carbon in sintered microcrystalline B 4 C (refs 7,16) (Fig.…”

“…Diamond anvil cell experiments suggested that the local amorphization of B 4 C, associated with non-hydrostatic stress states, takes place during unloading from a pressure above a critical value of B26 GPa 13 . In addition to shock loading and diamond anvil cell experiments, the amorphization has also been found when B 4 C is subjected to indentation and mechanical scratching [14][15][16][17] . These experimental observations demonstrated that the amorphous shear bands are the dominant deformation and failure modes of B 4 C at room temperature.…”

“…These experimental observations demonstrated that the amorphous shear bands are the dominant deformation and failure modes of B 4 C at room temperature. On the basis of computer simulations and spectroscopic investigations, several controversial models have been proposed to explain the formation of amorphous shear bands in the super-hard material 1,13,14,[16][17][18][19][20][21] . Nevertheless, the formation mechanisms of the amorphous shear bands still remain intensely debated owing to the lack of direct experimental observation with a sufficient spatial resolution to reveal the detailed structure of the amorphous bands.…”

Electronic structures and mechanical properties of boron and boron-rich crystals (Part I)

“…Pressure-induced amorphization is reported by Yan el al. [131]. In addition, dynamic indentation has been applied to see amorphization [132].…”