High pressure phase of pnictides yttrium YAs and YBi: first-principles studies

The high pressure phase transition in pnictides yttrium YAs and YBi has been investigated by a first-principles pseudopotential plane-wave method and density functional linear-response theory. Employing total energy calculations, the predicted rocksalt -> CsCl phase transition pressure is found, respectively, at 63.3 and 23 GPa for YAs and YBi. A pressure-induced soft transverse acoustic (TA) phonon mode is identified at 92 GPa for YAs and at 47 GPa for YBi. Phonon calculations suggest that YAs becomes dynamically instable with respect to the TA [epsilon 00] and TA [0 epsilon epsilon] phonon modes, while YBi becomes dynamically instable with respect to the TA phonon mode at the zone boundary X point. Furthermore, it is found that the increase of anti-bonding Y-4d bands significantly weakens the stability of the rocksalt phase of YAs and YBi under pressure inducing, hence a structural phase transformation.