Journal of Alloys and Compounds

(1)

First-principles prediction of the structural, elastic, thermodynamic, electronic and optical properties of Li

₄

Sr

₃

Ge

₂

N

₆

quaternary nitride

O. Boudrifa

^a

, A. Bouhemadou

^a,^⇑

, N. Guechi

^b

, S. Bin-Omran

^c,d

, Y. Al-Douri

^e

, R. Khenata

^f

aLaboratory for Developing New Materials and their Characterization, University of Setif 1, 19000 Setif, Algeria

bDepartment of Physics, Faculty of Science, University of Setif 1, 19000 Setif, Algeria

cDepartment of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia

dDepartment of Physics, Faculty of Science & Humanitarian Studies, Salman Bin Abdalaziz University, Alkharj 11942, Saudi Arabia

eInstitute of Nano Electronic Engineering, Universiti Malaysia Perlis, 01000 Kangar, Perlis, Malaysia

fLaboratoire de Physique Quantique et de Modélisation Mathématique (LPQ3M), Département de Technologie, Université de Mascara, 29000 Mascara, Algeria

a r t i c l e i n f o

Article history:

Received 28 April 2014

Received in revised form 13 August 2014 Accepted 14 August 2014

Available online 26 August 2014

Keywords:

Quaternary nitride First-principles calculations Elastic constants Electronic structure Optical properties Thermal properties

a b s t r a c t

Structural parameters, elastic constants, thermodynamic properties, electronic structure and optical properties of the monoclinic Li4Sr3Ge2N6quaternary nitride are investigated theoretically for the first time using the pseudopotential plane-wave based first-principles calculations. The calculated structural parameters are in excellent agreement with the experimental data. This serves as a proof of reliability of the used theoretical method and gives confidence in the predicted results on aforementioned properties of Li4Sr3Ge2N6. The predicted elastic constantsCijreveal that Li4Sr3Ge2N6is mechanically stable but aniso- tropic. The elastic anisotropy is further illustrated by the direction-dependent of the linear compressibility and Young’s modulus. Macroscopic elastic parameters, including the bulk and shear moduli, the Young’s modulus, the Poisson ratio, the velocities of elastic waves and the Debye temperature are numerically estimated. The pressure and temperature dependence of the unit cell volume, isothermal bulk modulus, volume expansion coefficient, specific heat and Debye temperature are investigated through the quasihar- monic Debye model. The band structure and the density of states of Li4Sr3Ge2N6are analyzed, which reveals the semiconducting character of Li4Sr3Ge2N6. The complex dielectric function, refractive index, extinction coefficient, absorption coefficient, reflectivity and electron energy-loss function are calculation for incident radiation polarized along the crystallographic directions and for energy up to 40 eV.

1. Introduction

Nitride materials have attracted signiﬁcant attention over the last 20 years due to their outstanding physical properties, which make them suitable for many technological applications such as:

ultraviolet photodetectors, blue light emitting diodes, lasers[1,2], converting solar light into electricity, photocatalytic, hydrogen production[3], lithium ion batteries[4], magnetic and electronic devices[5,6].

Owing to their great structural variety and superior material properties like luminescence, nonlinear optical properties, or lithium-ion conductivity, the ternary and multinary nitride compounds have received an increased level of attention[7–21]. The number of discovered ternary and quaternary nitrides has greatly expanded in recent years[22]. These new multinary materials provide a wider range of electrical, optical and chemical properties

responding the required properties by the technology applications.

The quaternary nitride compounds provide, for example, an extra degree of freedom to control the energy band gap and lattice constants as compared with ternary and binary materials[15]. Some of the numerous recently synthesized quaternary nitrides contain lithium as a constituent [5,10,17–20,22], such as Li4Sr3Ge2N6

[10]. Unfortunately, only a few numbers of the discovered quaternary nitrides have been fully characterized due to their propensity for hydrolysis or oxidation in air[10].

Park and colleagues[10]synthesized the quaternary nitride Li4-

Sr3Ge2N6as single crystals. It crystallizes in a monoclinic structure type, space group C2/m (No. 12 in the X-ray International Tables).

Apart the crystalline structure, information about the physical properties of the quaternary nitride Li4Sr3Ge2N6is scarce. In order to provide more detailed theoretical data of the fundamental physical properties, we present in this paper the results of ﬁrst-principles calculations of the structural, elastic, electronic, optical and thermodynamic properties of the Li₄Sr₃Ge₂N₆ quaternary nitride.

We provide a complete tensor of elastic constants of the

⇑Corresponding author. Tel./fax: +213 36620136.

E-mail address:[email protected](A. Bouhemadou).

Journal of Alloys and Compounds 618 (2015) 84–94

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Journal of Alloys and Compounds

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