Pressure-volume relation and pressure induced structural phase transformation in ytterbium pnictides

We have studied the pressure-volume relationship and pressure induced structural phase transformation in ytterbium pnictide compounds (YbN, YbP and YbAs) for the first time by using an interatomic potential approach based on the rigid ion model which considers only Coulomb and Born-Mayer type short-range interactions. The theoretically predicted pressure-volume relationship curves show that YbN, YbP and YbAs exhibit normal compression and undergo a NaCl to CsCl type structural transition at 164, 115 and 95 GPa, respectively, similar to the europium chalcogenides but contrary to their counterparts Yb chalcogenides for which the compression curve shows an anomalous behaviour due to the change in the valence state. The present study also confirms that these compounds behave similar to the simple rare earth europium chalcogenide compounds rather than the rare earth mixed valence compounds. A similar conclusion is also drawn from our earlier studies on the phonon properties for these compounds. The nature of the force constants at equilibrium and high pressure is discussed.