Universal Phase Transitions of AlB-Type Transition-Metal Diborides.

High-pressure phase transitions of AlB-type transition-metal diborides (TMB; TM = Zr, Sc, Ti, Nb, and Y) were systematically investigated using first-principles calculations. Upon subjecting to pressure, these TMB compounds underwent universal phase transitions from an AlB-type to a new high-pressure phase tP6 structure. The analysis of the atomistic mechanism suggests that the tP6 phases result from atomic layer folds of the AlB-type parent phases under pressure. Stability studies indicate that the tP6-structured ZrB, ScB, and NbB are stable and may be observed under high pressure and the tP6-structured TiB phase may be recovered at ambient pressure.