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Phase stability,mechanical and thermodynamic properties of orthorhombic and trigonal MgSiN2: an ab initio study
Authors:Fahima Arab  F. Ali Sahraoui  Abdelmadjid Bouhemadou  Layachi Louail
Affiliation:1. Laboratoire d'Optoélectronique et Composants, Département de Physique, Université de Setif 1, Sétif, Algeria;2. Unité de Recherche en Optique et Photonique (UROP), Université de Sétif 1, Centre de Développement des Technologies Avancées (CDTA), Alger, Algeria;3. Laboratory for Developing New Materials and their Characterization, Department of Physics, Faculty of Science, University of Setif 1, Setif, Algeria;4. Department of Physics and Astronomy, College of Science, King Saud University, Riyadh, Saudi Arabia;5. Unité de Recherche Matériaux émergents, University of Setif 1, Algeria
Abstract:Structural stability and mechanical and thermodynamic properties of the orthorhombic and trigonal MgSiN2 polymorphs (or-MgSiN2 and tr-MgSiN2) were investigated through density functional theory and quasi-harmonic Debye model (QHDM). Our calculations show that or-MgSiN2 is energetically the stable polymorph at low pressure, in agreement with previous experimental and theoretical study. Under pressure, a crystallographic transition from the orthorhombic structure to the trigonal one occurs around 25, 17.45 and 19.05 GPa as obtained from the generalized gradient approximation of Perdew-Wang (GGA-PW91), the generalized gradient approximation parameterized recently by Perdew et al (GGA-PBEsol) and the local density approximation developed by Ceperley and Alder and parameterized by Perdew and Zunger (LDA-CAPZ), respectively. Single-crystalline and polycrystalline elastic constants and related properties, namely Vickers hardness, acoustic Grüneisen parameter, minimum thermal conductivity, isotropic sound velocities and Debye temperature, were numerically estimated for both or-MgSiN2 and tr-MgSiN2. We have showed that the hardness of tr-MgSiN2 is comparable to that of the harder materials like c-BN and B6O. Temperature and pressure dependencies of volume, bulk modulus, thermal expansion, Grüneisen parameter, heat capacities and Debye temperature were investigated using QHDM.
Keywords:density functional theory  phase transition  thermodynamic properties  temperature and pressure effects
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