Chromium(III) boride, also known as chromium monoboride (CrB), is an inorganic compound with the chemical formula CrB.[1] It is one of the six stable binary borides of chromium, which also include Cr2B, Cr5B3, Cr3B4, CrB2, and CrB4.[2] Like many other transition metal borides, it is extremely hard (21-23 GPa),[3][4] has high strength (690 MPa bending strength),[4] conducts heat and electricity as well as many metallic alloys,[3][5][6] and has a high melting point (~2100 °C).[7][2] Unlike pure chromium, CrB is known to be a paramagnetic, with a magnetic susceptibility that is only weakly dependent on temperature.[8][9] Due to these properties, among others, CrB has been considered as a candidate material for wear resistant coatings and high-temperature diffusion barriers.Шаблон:Cn
It can be synthesized as powders by many methods including direct reaction of the constituent elemental powders,[10]self-propagating high-temperature synthesis (SHS),[4] borothermic reduction,[11][12] and molten salt growth.[13] Slow-cooling of molten aluminum solutions from high-temperatures has been used to grow large single crystals, with a maximum size of 0.6 mm x 0.6 mm x 8.3 mm.[3]
CrB has an orthorhombic crystal structure (space groupCmcm) that was first discovered in 1951,[14] and subsequently confirmed by later work using single crystals.[15] The crystal structure can be visualized as slabs face-sharing BCr6 trigonal prisms, in the ac-plane, that are stacked parallel to the <010> crystallographic direction. Similar to Cr3B4 and Cr2B3, the B atoms in the structure form covalent bonds with each other and are characterized by unidirectional B-B- chains parallel to the <001> crystallographic direction. The transition metal monoborides VB, NbB, TaB, and NiB have the same crystal structure. Шаблон:Cn
