Phase transition, structural and thermodynamic properties of Mg₂Si polymorphs

Abstract

The plane-wave pseudo-potential method within the framework of first principles is used to investigate the structural and elastic properties of Mg 2 Si in its intermediate pressure (Pnma) and high pressure phases (P 6 3 /mmc). The lattice constants, the band structures. The bulk moduli of the Mg 2 Si polymorphs are presented and discussed. The phase transition from anti-cotunnite to Ni 2 In-type Mg 2 Si is successfully reproduced using a vibrational Debye-like model. The phase boundary can be described as P = 24.02994 + 3.93 × 10 −3 T − 4.66816 × 10 −5 T 2 − 2.2501 × 10 −9 T 3 + 2.33786 × 10 −11 T 4 . To complete the fundamental characteristics of these polymorphs we have analysed thermodynamic properties, such as thermal expansion and heat capacity, in a pressure range of 0-40 GPa and a temperature range of 0-1300 K. The obtained results tend to support the available experimental data and other theoretical results. Therefore, the present results indicate that the combination of first principles and a vibrational Debye-like model is an efficient scheme to simulate the high temperature behaviours of Mg 2 Si.

Elastic Moduli: a Tool for Understanding Chemical Bonding and Thermal Transport in Thermoelectric Materials

“…Examples among functional materials include the ferroelectrics BaTiO 3 , SrTiO 3 , [212] EuTi 1À x Nb x O 3 [87] and Cd 2 Re 2 O 7 , [88] as well as several thermoelectrics such as Sn x Ge 1À x Te, [89,90,91] Zn 4 Sb 3 , [92] and Mg 2 Si. [93] Elasticity measurements have also been used to study superconducting transitions (e.g., Sr 2 RuO 4 , [94] YBa 2 Cu 3 O 7-δ , [95,96] and UPt 3 , [97] URu 2 Si 2 ). [98,99] Most of the examples in the literature are focused on low-temperature behaviors.…”

Phase transition and thermodynamic properties of BiFeO3from first-principles calculations

“…Thus, the aim of our study is to verify the occurrence of the pressureinduced phase transition from the initial trigonal structure with space group R3c to an orthorhombic structure with space group Pnma below 20 GPa, and to evaluate the thermodynamic properties of both phases. The quasi-harmonic Debye model, which well predicts various properties, [15][16][17][18][19][20] such as thermodynamic properties and the phase transition, has been selected for the purpose. To our best knowledge, it is the first time that the transition pressure from trigonal R3c-BiFeO 3 to orthorhombic Pnma-BiFeO 3 in the temperature range of 0-1200 K has been obtained theoretically.…”

Tensile properties of phase interfaces in Mg—Li alloy: A first principles study

“…With attention on environment protection and the energy crisis, Mg alloys, which have the lowest density of structural material, are commonly used in automobiles. [1][2][3][4][5][6][7] However, the applications of Mg alloys are limited due to their poor plasticity, for the crystal structure of Mg is hexagonally closepacked. The hexagonal close-packed structure (hcp) would transform into a body-centered cubic structure (bcc) with the addition of Li in Mg alloys, thus the plasticity of the Mg alloys could be improved and their density could be further reduced.…”