Novel Tungsten Triboride

A highly stable tungsten triboride with the Pearson symbol hP24 (hP24-WB3) is identified by using density functional theory calculations. This new structure can be derived from the well-known hP3 configuration by removing one third of tungsten atoms systematically so that the remaining tungsten atoms form three cycled layers of open hexagons with each a layer displaced by one atom. Such a porous and metallic system has an unexpectedly high Vickers hardness of 38.3 GPa. It is revealed that a three-dimensional covalent framework composed of hexagonal boron planes interconnected with strong zigzag W-B bonds is responsible for its unusual high hardness.