Universal Phase Transitions of AlB(2)-Type Transition-Metal Diborides

[Image: see text] High-pressure phase transitions of AlB(2)-type transition-metal diborides (TMB(2); TM = Zr, Sc, Ti, Nb, and Y) were systematically investigated using first-principles calculations. Upon subjecting to pressure, these TMB(2) compounds underwent universal phase transitions from an AlB(2)-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(2)-type parent phases under pressure. Stability studies indicate that the tP6-structured ZrB(2), ScB(2), and NbB(2) are stable and may be observed under high pressure and the tP6-structured TiB(2) phase may be recovered at ambient pressure.