On the microstructure of boron carbide

Evidence for multiple polytypes of semiconducting boron carbide (C2B10) from electronic structure

“…Electron and x-ray diffraction identification of exact crystal structures is a challenging problem given that carbon and boron have adjacent atomic numbers and low Z values. The structures of the two most well known boron carbide polytypes, based on the icosahedron, contain both direct and bridged links between adjacent icosahedra [6][7][8]10]. The possible existence of such bridging links adds a number of opportunities for different carbon atom placement in the lattice, though these bridging links are not compellingly evident in our data.…”

“…The distances of the diffraction spots or rings from the centre of such patterns correspond to the interplanar spacings within each crystal. While there is close agreement with interplanar spacings in known boron-carbon polytypes and between the fitted radii of boron carbide rings (figures 5(c) and (d)) [23], these diffraction data do not match completely with known polytypes [5][6][7][8][9][10][11]. We cannot at this point directly relate the different structural polytypes of the C 2 B 10 boron carbides with the those polytypes identified by electronic structure.…”

“…Nonetheless, the consensus is that the building block of all these materials is based on the icosahedron [1][2][3][4][5][6][7][8][9][10][11]. There are very strong indications from electronic structure studies [5,12,13] that there are several polytypes for the 'C 2 B 10 ' material.…”

“…Generally these different polytypes have been associated with changing composition such as increasing the boron concentration [3,4,6,10,[24][25][26][27][28][29][30][31][32][33][34] or replacing carbon with other main group elements such as phosphorus [35,36], aluminium [37][38][39][40][41] and other main group elements. We have identified different polytypes of the semiconducting boron carbides with large direct band gaps (materials formed from para-carborane and dimeric phosphorus bridged ortho-carborane (C 2 B 10 H 10 PCl) 2 ) and those with smaller band gaps (materials formed from ortho-carborane and meta-carborane).…”

The incorporation of Nickel and Phosphorus dopants into Boron-Carbon alloy thin films

“…Like crystalline boron carbide, the boroncarbon alloys consist of an icosahedral network [1,8], where the icosahedra are composed of boron and carbon atoms. In contrast, the icosahedra in crystalline boron carbide, are almost exclusively constructed from boron atoms with the carbon atoms predominantly participating in the three atom chains that connect the icosahedral network [9][10][11][12][13][14][15][16]. The average crystallite size of the PECVD-grown alloys is approximately 100 Å [1,8].…”