Full Length ArticleStructural, electronic, dynamic, optic and elastic properties of MgScGa via density functional theory
Introduction
In the present era, energy and energy sources are in great importance, in particular the renewable energy sources. The main renewable energy source is the sun and the scientists try to find alternative renewable energy sources. One of the alternative source is the thermoelectric waste heat recovery in which the thermoelectric materials are used. Thermoelectric materials are able to convert any kind of waste heat (thermal) energy into electrical energy and also electrical energy to thermal energy [1]. The origin of the waste heat can be anywhere such as; home heating, automotive exhaust, ignition of fossil fuels, sun, or chemical and nuclear reactions, etc. Hence, thermoelectric waste heat recovery has an important effect in reducing the impact of global climate change and environmental pollution [[2], [3], [4]] and also reducing the dependence on fossil fuels [5].
Among the thermoelectric materials, Heusler and half- Heusler compounds are up-and-coming nominees because of their good thermal stabilities, high power performance and effective mechanical properties [6]. The form of Heusler alloys are like X2YZ in the L21 structure parent compound consisting of four interpenetrating fcc sublattices, the half-Heusler alloys occur when one of the two equivalent sites of X atom is vacant. In other words, the form of the half –Heusler alloys is like XYZ in the C1b structure [7,8]. The half-Heusler alloys crystallize in cubic structure, with the F3m space and 3 m point groups (no. 216) [6]. Also, ground state properties of Heusler compounds can be predicted by only determining the number of valence electrons [9]. The half-Heusler compounds with VE = 18 are diamagnetic semiconductors and when the valence electron number is VE = 17 or 19, the system became paramagnetic or ferromagnetic metal [8,10,11].
In this study we investigated MgScGa compound which is a half-Heusler alloy [12]. The number of valence electrons of MgScGa compound is 18, as mentioned above, our material is said to be a diamagnetic semiconductor. Our motivations are firstly, its importance with respect to the thermoelectric properties of this alloy and secondly, any of the physical properties that we studied in this work are not investigated in detail before. The second motivation is also the novelty of our work. There are many experimental and theoretical studies in the literature in which the structural and electronic properties of ternary alloys containing both Sc and Ga are expressed [[13], [14], [15], [16], [17]]. However, there is only one study belongs to T. Gruhn [12], that we come across with our deeply investigation in the literature about the MgScGa compound. In that study Gruhn investigated the equilibrium lattice parameters of a big number of half-Heusler compounds. He has just given the value of the lattice parameters but we investigated the structural properties of the MgScGa compound by calculating the bulk modulus, derivative of bulk modulus and the lattice parameters. We also plotted the conventional cell of MgScGa compound. Then we examined the electronic properties of the MgScGa compound by plotting its electronic band structure and electronic density of states graphs. After all we investigated the dynamic properties by obtaining the phonon band and phonon density of states (PHDOS) graphs and performing a factor group analysis we obtained the irreducible representation of Γ of MgScGa compound. We also deeply investigated the optic and elastic properties of MgScGa compound and we discussed all these results in the Results and Discussion section.
Section snippets
Materials and method
Structural, electronic and dynamic properties of the MgScGa compound have been studied with the Density Functional Theory (DFT). This study was carried out using the Generalized Gradient Approximation (GGA) [18]. The calculation of the structural and phonon properties were carried out using the Quantum Espresso [19] package program. The investigation of electronic, optic and elastic properties were done by using the ABINIT [20] programme. The wave functions have been extended to the plane wave
Results and discussion
In this study, first, we investigated the structural properties of MgScGa compound. MgScGa compound is in a zinc blende structure with F3m space (No.216) and 3 m point () groups. We presented the conventional cell of MgScGa compound in Fig. 1 by using VESTA [23] computer programme. MgScGa compound has only three atoms in its primitive cell. Total energy of this compound was calculated as a function of volume, and we obtained total energy versus volume graph. This graph was fitted to the
Conclusions
Theoretical investigation based on density functional theory is performed to investigate structural, electronic and dynamic properties of MgScGa compound. The value of calculated lattice parameter is very close to the value of the literature. The basic structural paramaters such as bulk modulus and the pressure derivative of the bulk modulus have been calculated for the first time. In order to investigate the electronic structure we obtained electronic band structure of MgScGa compound and we
Author statement
The corresponding author is responsible for ensuring that the descriptions are accurate and agreed by all authors.
Declaration of competing interest
We confirm that there is no conflict of interest between the authors.
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