Electronic Structure of Sodium Thiogermanate

Dmytro Ivanovych Bletskan,Vasyl Mykolaiovych Kabatsii,Vasyl Vasyliovych Vakulchak

doi:10.4236/ojinm.2015.52004

Dmytro Ivanovych Bletskan, Vasyl Mykolaiovych Kabatsii + Show 1 more

Open Access

https://doi.org/10.4236/ojinm.2015.52004

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Abstract

Ab initio calculations of the band structure, total and partial densities of states and the spatial distribution of the electron charge density of crystalline Na2GeS3 are performed in the framework of density functional theory in the local density approximation for an exchange-correlation potential. According to the calculation results, sodium thiogermanate is a direct-gap crystal with the top of the valence band and the bottom of the conduction band at the point of the Brillouin zone. The calculated band gap is Eg= 2.51 eV. The nature of the components of the electronic states in different subbands of the valence band is determined. The calculated total density of states in the valence band of the crystal is compared with the known experimental X-ray photoelectron spectrum of Na2GeS3 glass. Based on the maps of the electron density distribution, the nature of the chemical bonds and high mobility of Na+ ions in Na2GeS3 crystal is analyzed.

Highlights

In the recent years, an intense work is underway to search for electrode materials for sodium-ion batteries that could in future replace lithium-ion power sources [1]
We report on the density functional theory (DFT) calculations of the energy band structure, total and partial local densities of states and the spatial distribution of the electron density for crystalline Na2GeS3
The valence bands have a weak dispersion and consist of three energy separated band bunches of (VBI, VBII, VBIII, numbering from the top subband), which correspond to discrete bands in the density of states N(E) spectra

Summary

Introduction

An intense work is underway to search for electrode materials for sodium-ion batteries that could in future replace lithium-ion power sources [1]. Even though physical and chemical properties, including the ionic conductivity, of glassy and crystalline Na2GeS3 are studied rather well [2]-[7], the knowledge of such important characteristics as optical, vibrational, and mechanical ones is still quite limited. One of the main reasons for the lack of such data is high hygroscopicity of this material In such situation, theoretical methods, above all the calculations of Na2GeS3 electronic structure, seem to play an increasing role because the important properties of ionic crystals are determined by the peculiarities of their crystal and electronic structure. The knowledge of the electronic structure will help one to determine the nature of the Na-S chemical bonds required for a better understanding of the glass local structure and the mechanism of the ionic conductivity

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Results

Conclusion