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Abstract
Pressure-induced structural aspects of NaCl-type (B1) to CsCl-type (B2) structures in yttrium pnictides (YX; X = N, P and As) are presented. An effective interionic interaction potential with the long-range Coulomb and van der Waals (vdW) interaction and the short-range repulsive interaction up to second-neighbor ions within the Hafemeister and Flygare approach with a modified ionic charge is developed. Particular attention is devoted to evaluate the vdW coefficients following the Slater–Kirkwood variational method, as both the ions are polarizable. Our results on vast volume discontinuity in the pressure–volume phase diagram identify the structural phase transition from B1 to B2 structure. The estimated value of the phase-transition pressure (P t) and the magnitude of the discontinuity in volume at the transition pressure are consistent when compared with the reported data. The variations of elastic constants and their combinations with pressure follow a systematic trend identical to that observed in other compounds of the NaCl-type structure family, and the Born relative stability criteria are valid in yttrium pnictides.
Acknowledgements
Financial support from National Science Council of Taiwan (NSC-96-2112-M-259-003) and Madhya Pradesh Council of Science and Technology, Bhopal, India, is gratefully acknowledged.