Boron under Pressure: Phase Diagram and Novel High-pressure Phase

Boron has a unique chemistry, responsible for remarkable complexities even in the pure element. I review some of the history of the discovery of this element, and recent surprises found in boron under pressure. I discuss the recent discovery of a new high-pressure phase, γ-B28, consisting of icosahedral B12 clusters and B2 pairs in a NaCl-type arrangement: (B2)(B12), and displaying a significant charge transfer δ ~ 0.48. Boron is the only light element, for which the phase diagram has become clear only in the last couple of years, and this phase diagram is discussed here among other recent findings.