Predicted Suppression of the Superconducting Transition of New High-Pressure Yttrium Phases with Increasing Pressure from First-Principles Calculations

Structure searches for new high-pressure phases of Y metal have been performed by using evolutionary algorithms in conjunction with a first-principles, pseudopotential plane-wave method based on density functional theory. The oF16-Fddd and hP3-P3(1)21 phases are predicted to be energetically favorable at pressures over 97 GPa. These two phases are shown to be dynamically stable by computing their phonon dispersions. We thus propose that oF16-Fddd and hP3-P3(1)21 are the most probable crystal structures Y may take in the 97-206 GPa range. The superconducting critical temperatures (T-c) of the new phases are estimated using the Allen-Dynes formula. The T-c is predicted to decrease with increasing pressure over about 100 GPa, in sharp contrast to its observed monotonic increase under lower pressure. The electronic origins of the stabilities of the proposed high-pressure phases have also been investigated.