Advances in Physics Theories and Applications www.iiste.org ISSN 2224-719X (Paper) ISSN 2225-0638 (Online) Vol.19, 2013 - Selected from International Conference on Recent Trends in Applied Sciences with Engineering Applications 90 High Pressure Structural Properties of Rare-earth Antimonide Namrata Yaduvanshi and Sadhna Singh Department of Physics, Barkatullah University, Bhopal [M.P.] Email : namrata_yaduvanshi@yahoo.com Abstract In the present paper, we have investigated the high-pressure structural phase transition of rare-earth antimonide. We studied theoretically the structural properties of this compound (DySb) by using the three-body potential model with the effect of electronic polarizability (TBIPE P ). These compounds exhibits first order crystallographic phase transition from NaCl (B 1 ) to CsCl (B 2 ) phase at 22.6 GPa respectively. The phase transition pressures and associated volume collapse obtained from present potential model(TBIPE P ) show a good agreement with available experimental data. Keywords: High Pressure, Crystal Structure, Volume Collapse 1. Introduction The mono-antimonide of rare earths with NaCl structure in recent years have drawn great attention of condensed matter scientists because of their diversive and unusual properties, in respect of structural, magnetic and vibrational properties [1]. So far as the structural properties are concerned, several pnictides of lanthanide group, which crystallize in NaCl (B1) type crystal structure have been investigated by using high-pressure X-ray diffraction technique [2-5] and reported to undergo to either CsCl (B2) or body centered tetragonal structure. These partially filled f-electron shells of the lanthanide ions are highly delocalized and therefore interact strongly with the lattice. Such behaviour has been interpreted in terms of promotion of 4f electron of rare earth ion to the 5d conduction band and the mixing of f states with the p states of the neighbouring ion. The electronic band structures of NdY and CeY (Y:pnictogen) have been calculated by De et al.[6] using self consistent semi relativistic Linear Muffin-Tin Orbital Method reveals that the unusual properties are due to strong mixing of f- states of rare earth ion with the p-orbital of pnictogen ion (p–f mixing) [6,7]. The high pressure form of lighter lanthanide antimonides (RESb, RE=La,Ce, Pr and Nd) is reported to be body centered tetragonal where as the structure of middle RESb (RE=Sm, Gd and Tb) is unknown. The heavier RESb (RE= Dy, Ho, Er, Tm and Lu) show B1- B2 phase transition [8]. In the present paper we have investigated the high-pressure structural phase transition, cohesive and elastic properties of rare earth antimonide DySb. We have employed our three body interaction potential with the effect of electronic polarizability(TBIPE P ) approach to study high pressure behavior. The present three body potential model includes the long range Columbic, three body interaction, short range overlap repulsive interaction operative up to second neighbor ions within Hafemeister and Flygare approach [9] and electronic Polarizibilities effect. The importance of inclusion short range (SR), and electronic polarizability has been established in our work. 2. Potential Model and Method of Calculation: It is well known that the application of pressure on crystals results a change in its volume that leads to an increased charge transfer (or three-body interaction effects) due to the deformation of the overlapping electron shells of the adjacent ions. The three body interaction arises during lattice vibrations when electron shells of neighboring ions overlap. This overlapping leads to the transfer of charge which interacts with other charges and many body interaction (MBI) takes place, the dominant part of which is the three body interaction. This interaction becomes more important due to the decrease in inter ionic spacing of the lattice crystal when pressure gets increased and when anions experience sufficient overlap. Besides, both an enhancement in overlap energy and the transferred charge due to the overlap in electron shells modify the ionic charge, which in its turns modifies the Coulomb energy. The expression for the modified Coulomb energy due to three body interaction (TBI) is Φ m (r 0 ) = Φ c + Φ T (1) Φ m (r 0 ) = [-α M Z 2 e 2 / r] [1+(2n/Z) f(r 0 )] (2) Here α M is the Madelung constant (for NaCl and for CsCl structure solids), r 0 is the equilibrium nearest neighbor (nn) ion separation, n is the number of nearest neighbor (nn), and f(r) is the TBI parameter which is dependent on the nearest neighbor distance (r) as f(r) = f 0 exp (-r/ρ) (3) These effects have been incorporated in the Gibbs free energy (G=U+PV-TS) as a function of pressure (P). Here, U is the internal energy, which at T= 0 K is equivalent to the lattice energy and S is the vibrational entropy at absolute temperature T. Since theoretical calculations are done at T= 0 K, the Gibbs’s free energy is equivalent