ATOMIC STRUCTURE OF BORON CARBIDE

Boron carbide is composed of only boron and carbon, two light solid elements. Due to the weak scattering power detection of light elements by using microscopes, the atomic structure of boron carbide, the third hardest naturally occurring material is unresolved and hotly debated. In this chapter we show the atomic structure of boron carbide by using stateof-the-art spherical abberation corrected scanning transmission electron microscopy combined with a newly developed annular bright field imaging mode. From the experiments, we found three different crosslinked linear chain structures i.e., C-B-C, C-V-C and C-C-C polytypes. The measurements from atomic images revealed presence of about 80-85% C-B-C cross-linked linear chains suggesting that this polytype unit is thermodynamically favorable in boron carbide ground state binary phase. The deviation from ideal C-B-C cross-linked linear chain structure may have been related to high temperature solid solubility.