A study of the phase transitions electronic structures and thermodynamic properties of mg2x x ge si and sn under high pressure

Journal of Science: Advanced Materials and Devices (2017) 105e114 Contents lists available at ScienceDirect Journal of Science: Advanced Materials and Devices journal homepage: www.elsevier.com/locate/jsamd Original Article A study of the phase transitions, electronic structures and thermodynamic properties of Mg2X (X ¼ Ge, Si and Sn) under high pressure M Guezlane a, H Baaziz b, *, Z Charifi b, A Belgacem-Bouzida c, Y Djaballah c a Department of Physics, Faculty of Science, University of Batna, 05000, Batna, Algeria Physics Department, Faculty of Science, University of M'sila, 28000, M'sila, Algeria Laboratoire d' etude Physico-Chimique des Mat eriaux, D epartement de Physique, Facult e des Sciences, Universit e de Batna, Rue Chahid Boukhlouf, 05000, Batna, Algeria b c a r t i c l e i n f o a b s t r a c t Article history: Received 19 November 2016 Received in revised form 21 January 2017 Accepted 26 January 2017 Available online February 2017 In this work, we theoretically investigate phase transitions, electronic structures and thermodynamic properties of Mg2X (X ¼ Ge, Si and Sn) under high pressures To reach this goal, the total energy has been calculated by using the full-potential linearized augmented plane wave (FP-LAPW) method with generalized gradient approximation (GGA), local density approximation (LDA) and EngeleVosko approximation (EV-GGA), which are based on the exchange-correlation energy optimization The fully relaxed structure parameters of Mg2X compounds are in good agreement with the available experimental data Our results demonstrate that the Mg2X compounds undergo two pressure-induced phase transitions The first one is from the cubic antifluorite (Fm3m) structure to the orthorhombic anticotunnite (Pnma) structure in the pressure range of 3.77e8.78 GPa (GGA) and 4.88e8.16 GPa (LDA) The second transition is from the orthorhombic anticotunnite structure to the hexagonal Ni2Intype (P63 mmc) structure in the pressure range of 10.41e29.77 GPa (GGA) and 8.89e63.45 GPa (LDA) All the structural parameters of the high pressure phases are analyzed in detail Only a small difference in the structural parameters is observed at high pressures between the calculated and experimental results The electronic and thermodynamic properties are also analyzed and discussed The establishment of the metallic state of the Mg2X (X ¼ Ge, Si and Sn) compounds at high pressure is confirmed © 2017 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) Keywords: DFT FP-LAPW EV-GGA Phase transitions Thermodynamic Introduction Among the silicides, Mg2Si is the only possible stoichiometric compound in the MgeSi alloy as well as Mg2Sn and Mg2Ge These compounds have attracted much attention in the last few years due to their important properties Their relatively high melting points (1358 K [1], 1030 K [1] and 1390 K [2] for Mg2Si, Mg2Sn and Mg2Ge, respectively) and high electrical conductivity make them very useful for high thermoelectric material applications in the temperature range of 500e800 K [3,4] The Mg2X (X ¼ Ge, Si and Sn) compounds as lightweight materials with high specific strengths and high specific elastics modulus [5] were proposed to be suitable * Corresponding author Fax: ỵ213 35556453 E-mail address: baaziz_hakim@yahoo.fr (H Baaziz) Peer review under responsibility of Vietnam National University, Hanoi materials for the automotive products and manufacturing processes, and due to the narrow energy gaps (Eg ~ 0.3e0.6 eV) [6] they can be used as an infrared detector in the wavelength range from 1.2 to 1.8 mm [6] Finally, the non-toxic properties make them environmentally friendly [7] Under ambient conditions (the pressure below 0.1 MPa), the Mg2X (X ¼ Ge, Si and Sn) compounds are intermetallic with low densities (