Universal Phase Transitions Of Alb2-Type Transition-Metal Diborides

High-pressure phase transitions of AlB2-type transition-metal diborides (TMB2; TM = Zr, Sc, Ti, Nb, and Y) were systematically investigated using first-principles calculations. Upon subjecting to pressure, these TMB2 compounds underwent universal phase transitions from an AlB2-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 AlB2-type parent phases under pressure. Stability studies indicate that the tP6-structured ZrB2, ScB2, and NbB2 are stable and may be observed under high pressure and the tP6-structured TiB2 phase may be recovered at ambient pressure.