Tantalum borides are compounds of tantalum and boron most remarkable for their extreme hardness.
The Vickers hardness of TaB and TaB2 films and crystals is ~30 GPa. Those materials are stable to oxidation below 700 °C and to acid corrosion.
TaB2 has the same hexagonal structure as most diborides (AlB2, MgB2, etc.). The mentioned borides have the following space groups: TaB (orthorhombic, Thallium(I) iodide-type, Cmcm), Ta5B6 (Cmmm), Ta3B4 (Immm), TaB2 (hexagonal, aluminum diboride-type, P6/mmm).