Due to the outstanding properties of chromium borides and their use in various applications, they have been studied extensively both experimentally and theoretically. In chromium boride systems, seven solid state phases have been observed: Cr2B (space group Fddd with the Mg2Cu structure; space group I4/mcm with the Al2Cu structure), Cr5B3 (space group I4/mcm), CrB (space group I41/amd with the MoB structure; space group Cmcm with the TiI structure), Cr3B4 (space group Immm), Cr2B3 (space group Cmcm), CrB2 (space group P6/mmm with the AlB2 structure), and CrB4 (space group Immm). 

Among these borides, CrB, Cr3B4, and CrB2 were characterized by high melting points and decomposition temperatures of 2100, 2070, and 2200 ℃, respectively. This article will show the crystal structure of CrB system.

Figure 1. Crystal structures of chromium borides in CrB systems. 

The figure above shows the crystal structure of some chromium borides. The gray and black spheres represent Cr and B atoms, respectively. 

a) CrBMoB, no. 141; the B atom is located at 8e (0, 1/2, 0.032) and the Cr atom is at 8e (0, 1/2, 0.177). 

b) CrBTiI, no. 63; the B atom is located at 4c (0, 0.064, 1/4) and the Cr atom is at 8h (0, 0.3543, 1/4).

c) CrB3PSA, no. 187; the B atoms are located at 1b (0, 0, 1/2), 2h (1/3, 2/3, 0.3156), and the Cr atom is at 1a (0, 0, 0). 

d) CrB3PSB, no. 47; the B atoms are located at 1e (0, 1/2, 0), 2t (1/2, 1/2, 0.2517), and the Cr atom is at 1c (0, 0, 0.5).

Reference

[1] Phase Stability and Elastic Properties of Chromium Borides with Various Stoichiometries. DOI:10.1002/cphc.201201009