Boron carbide under torsional deformation: evidence of the formation of chain vacancies in the plastic regime

TL;DR

This study combines experimental and theoretical methods to reveal that torsional deformation induces chain vacancies and amorphous zones in boron carbide at high pressure, affecting its structural integrity.

Contribution

It provides new evidence of chain vacancy formation in boron carbide under torsional stress using combined DFT calculations and advanced characterization techniques.

Findings

Detection of boron vacancies in intericosahedral chains

Identification of amorphous zones post-deformation

Correlation between deformation and defect formation

Abstract

We report a combined experimental and theoretical study of boron carbide under stress/deformation. A special rotating anvil press, the rotating tomography Paris Edinburgh cell (RotoPEC), has been used to apply torsional deformation to boron carbide under a pressure of 5~GPa at ambient temperature. Subsequent damages and point defects have been analysed at ambient pressure by energy dispersive X-ray microdiffraction at the synchrotron and by Raman spectroscopy, combined with calculations based on the density functional theory (DFT). We show that apart from the signals due to B$_4$C, new peaks appear in both characterisation methods. The DFT calculations of atomic structures and phonon frequencies enable us to attribute most of the new peaks to boron vacancies in the intericosahedral chains of boron carbide. Some of the Raman spectra also show three peaks that have been attributed to amorphous boron carbide in the literature. Deformed boron carbide thus shows small inclusions of clusters of boron carbide with chain vacancies, and/or small zones interpreted as amorphous zones.