Magnesium diboride (MgB2) is a simple ionic binary compound that has proven to be an inexpensive and useful superconducting material.
Rhenium diboride (ReB2) is a synthetic superhard material. It was first synthesized in 1962 and re-emerged recently due to hopes of achieving high hardness comparable to that of diamond. However, the ultrahigh hardness has not been confirmed.
Titanium diboride (chemical formula TiB2) is an extremely hard ceramic compound composed of titanium and boron which has excellent resistance to mechanical erosion. TiB2 is also a reasonable electrical conductor, an unusual property for a ceramic, so it can be used as a cathode material in aluminium smelting and can be shaped by electrical discharge machining.
Zirconium diboride (ZrB2) is a highly covalent refractory ceramic material with a hexagonal crystal structure. ZrB2 is an Ultra High Temperature Ceramic (UHTC) with a melting point of 3246 °C.