High Pressure Structural Phase Transition and Elastic Properties of MgX (X = S, Se, Te) Semiconducting Compounds
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0987-PP03-14
High Pressure Structural Phase Transition and Elastic Properties of MgX (X = S, Se, Te) Semiconducting Compounds Dinesh Varshney1, Netram Kaurav2, Kamal Kumar Choudhary3, R. Kinge1, and R. K. Singh4 1 School of Physics, Devi Ahilya University, Khandwa Road Campus, Indore, 452001, India 2 Department of Physics, Institute of Science and Laboratory Education, IPS Academy, A. B. Road, Rajendra Nagar, Indore, 452012, India 3 Department of Engg. Physics, S. V. I. T. S., Sanwer Road, Baroli, Indore, 453331, India 4 Institute of Professional and Scientific Studies and Research, Choudhary Devilal University, Sirsa, 125055, India
ABSTRACT Pressure-induced structural aspects of NaCl-type (B1) to CsCl-type (B2) structure in MgX [X = S, Se, Te] semiconductors are presented. An effective interionic interaction potential (EIOP) with long range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction upto second-neighbor ions within the Hafemeister and Flygare approach is developed. Particular attention is devoted to evaluate the vdW coefficients following the variational method, as both the cation and the anion are polarizable. Our result on vast volume discontinuity in pressure volume phase diagram identifies the structural phase transition from B1 to B2 structure. The estimated value of the phase transition pressure (Pt) is consistent with results previously published. The variations of elastic constants with pressure follow a systematic trend identical to that observed in others compounds of NaCl type structure family. INTRODUCTION The alkaline-earth chalcogenides II-VI compounds (AX: A = Be, Mg, Ca, Sr, Ba; X = O, S, Se, Te) form a very important closed-shell ionic system crystallized in the NaCl-type (B1) structure at ambient conditions. Magnesium chalcogenides MgX (X = S, Se, Te) have received much study in recent past due to their unusual thermodynamical properties related to structural phase transitions [1 - 4]. Ruoff et al. [4] have investigated MgSe using energy dispersive X-ray diffraction up to 202 GPa. They also perform band structure calculations mainly local density approximation and ultra soft pseudopotential pressure up to 500 GPa. MgSe undergoes a continuous phase transformation from the rocksalt to FeSi (B28) beginning at around 99 ± 8 GPa and approaching sevenfold coordination at 202 GPa. Further theoretical computation finds the B28 transition beginning at 58 GPa followed by a transition to an orthorhombic distortion of the B2 structure at 429 GPa [4]. Furthermore, from an empirical map based on the transition pressure in binary chalcogenides versus the ratio of cation to anion ionic radii of Ba, Sr and Ca the B1 to B2 transformation is expected as follows: MgSe (175 GPa), MgS (172 GPa), MgO (210 GPa), if no other transition intervenes [1]. However, a detailed description of the electronic band structures of MgS and MgSe were investigated using TB-LMTO method [5] and are found to undergo a structural phase transition from the zincblende (B3) to B1 structure at pressures
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