Structural analysis and valence variation in ytterbium pnictides YbX (X=P, As) under high pressure

• The (NaCl) B1to CsCl (B2) phase transition was found at 51 GPa and 51.8 GPa for YbP and YbAs respectively.
• Elastic, mechanical and anharmonic properties are computed using an improved interaction potential model (IIPM) probably for the first time.
• The pressure dependence of structural and elastic properties has been discussed.
• Debye temperatures, Gruneisen parameter, the longitudinal and transverse sound velocity for YbX are calculated.
• YbX compounds behave similar to cerium pnictide compounds and trivalent in nature.

We have studied the pressure induced structural phase transition, pressure volume relationship and valence variation in ytterbium pnictide compounds (YbX; X=P, As). An improved interaction potential model (IIPM) (including the polarizability effect) has been applied. We have also studied the trivalent and intermediate valence in ytterbium compounds and predicted the phase transition pressures, volume collapses for two different valences. The variations of the second-order elastic constants with pressure and stability condition have shown systematic trends in YbX compounds similar to those observed in other compounds of NaCl structure. The pressure volume relationship curves show that ytterbium pnictide compounds undergo NaCl to CsCl type structural transition. The present study also confirms that these compounds behave similar to the rare earth cerium pnictide compounds and they are trivalent in nature.