Boride

A boride is a compound between boron and a less electronegative element, for example silicon boride (SiB₃ and SiB₆). The borides are a very large group of compounds that are generally high melting and are covalent more than ionic in nature. Some borides exhibit very useful physical properties. The term boride is also loosely applied to compounds such as B₁₂As₂ (N.B. Arsenic has an electronegativity higher than boron) that is often referred to as icosahedral boride.

The borides can be classified loosely as boron rich or metal rich, for example the compound YB₆₆ at one extreme through to Nd₂Fe₁₄B at the other. The generally accepted definition is that if the ratio of boron atoms to metal atoms is 4:1 or more if the compound is boron rich, if it is less, then it is metal rich.

The main group metals, lanthanides and actinides form a wide variety of boron-rich borides, with metal:boron ratios up to YB₆₆.

The properties of this group vary from one compound to the next, and include examples of compounds that are semi conductors, superconductors, diamagnetic, paramagnetic, ferromagnetic or anti-ferromagnetic. They are mostly stable and refractory.

Some metallic dodecaborides contain boron icosahedra, others (for example yttrium, zirconium and uranium) have the boron atoms arranged in cuboctahedra.

LaB₆ is an inert refractory compound, used in hot cathodes because of its low work function which gives it a high rate of thermionic emission of electrons; YB₆₆ crystals, grown by an indirect-heating floating zone method, are used as monochromators for low-energy synchrotron X-rays.

...
Wikipedia