Journal of Physics and Chemistry of Solids 69 (2008) 60–69 Phase transformation and elastic behavior of MgX (X ¼ S, Se, Te) alkaline earth chalcogenides Dinesh Varshney a,Ã , N. Kaurav b , U. Sharma a , R.K. Singh c a School of Physics, Vigyan Bhawan, Devi Ahilya University, Khandwa Road Campus, Indore 452001, India b Department of Physics, Institute of Science and Laboratory Education, IPSA, Rajendra Nagar, Indore 452012, India c Institute of Professional, Scientific Studies, and Research, Choudhary Devi Lal University, Sirsa 125055, India Received 22 February 2007; received in revised form 21 May 2007; accepted 24 July 2007 Abstract Pressure induced structural aspects of NaCl-type (B1) to CsCl-type (B2) structure in alkaline earth chalcogenides (AECs) magnesium chalcogenides (MgX; X ¼ S, Se, and Te) are presented. An effective interionic interaction potential (EIoIP) with long-range Coulomb interactions and the Hafemeister and Flygare type short-range overlap repulsion extending up to the second neighbor ions and the van der Waals (vdW) interaction is developed. The vdW coefficients are evaluated following the Slater–Kirkwood variational method, as both the ions are polarizable. The present calculations have revealed reasonably good agreement with the available experimental data on structural transition (B1–B2 structure), the phase transition pressures P t of 167 (MgS), 170 (MgSe), and 176 (MgTe) GPa as well the elastic properties. The calculated values of the volume collapses [DV(P)/V(0)] are also closer to their observed data. Further, the variations of the second and third order elastic constants with pressure have followed a systematic trend, which are almost identical to those exhibited by the observed data measured for other semiconducting compounds with rocksalt (B1) type crystal structure. The Born and relative stability criteria is valid in Mg monochalcogenides. r 2007 Elsevier Ltd. All rights reserved. PACS: 05.70.f; 62.20.d; 65.50 Keywords: D. Phase transitions; D. Thermodynamic properties 1. Introduction The promising potential of alkaline earth chalcogenides (AECs) used for luminescent devices has led to extensive studies, both theoretical and experimental. High-pressure research on structural phase transformations and behavior of materials under compression based on their calculations or measurements have become quite interesting in the recent few years as it provides insight into the nature of the solid-state theories, and determine the values of funda- mental parameters. Mixed crystals of AECs with wide energy gap II–VI compounds have attracted much atten- tion in view of the increasing need of potentially good semiconductors for various electrical and optical devices. Applied research emphasized in studying the tempera- ture (pressure) dependence of their physical properties with a view in preparing the material to exhibit the expected properties in specific conditions of thermal and mechanical stress environment. The AECs II–VI compounds (AX: A ¼ Be, Mg, Ca, Sr, Ba; X ¼ O, S, Se, Te) form a very important closed-shell ionic system crystallized in the NaCl-type (B1) structure at ambient conditions [1–4]. These compounds crystallize at room temperature in fourfold-coordinated cubic zinc-blende structure [1]. Elec- tronic band structure studies of these systems specifies that there are no d electrons available in the valence band and a energy gap of about 2.5–6 eV is documented. Under compression, a first-order phase transition from the sixfold-coordinated B1 structure to the eightfold-coordi- nated CsCl-type (B2) has been found in magnesium chalcogenides MgX (X ¼ S, Se, and Te) [5–10]. ARTICLE IN PRESS www.elsevier.com/locate/jpcs 0022-3697/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2007.07.121 Ã Corresponding author. Tel./fax: +91 7312465689. E-mail address: vdinesh33@rediffmail.com (D. Varshney).