Ab-initio study of structural, vibrational and optical properties of solid oxidizers

TL;DR

This study provides a comprehensive ab-initio analysis of the structural, vibrational, and optical properties of solid oxidizers MNO$_3$ and MClO$_3$, revealing insights into their phase stability, bonding, and spectral characteristics.

Contribution

It introduces accurate predictions of structural and vibrational properties using dispersion-corrected methods and analyzes optical spectra, expanding understanding of these solid oxidizers.

Findings

Materials are wide band gap insulators with ionic and covalent bonding.

Vibrational frequencies show a red-shift with increasing atomic mass.

Optical spectra indicate nitrate/chlorate group transitions below 20 eV.

Abstract

We report the structural, elastic and vibrational properties of five ionic-molecular solid oxidizers MNO$_3$ (M = Li, Na, K) and MClO$_3$ (M = Na, K). By treating long range electron-correlation effects, dispersion corrected method leads to more accurate predictions of structural properties and phase stability of KNO$_3$ polymorphs. The obtained elastic moduli show soft nature of these materials and are consistent with Ultrasonic Pulse Echo measurements. We made a complete assignment of vibrational modes which are in good accord with available experimental results. From calculated IR and Raman spectra, it is found that the vibrational frequencies show a red-shift from Li -> Na -> K (Na -> K) and N -> Cl for nitrates (chlorates) due to increase in mass of metal and non-metal atoms, respectively. The calculated electronic structure using recently developed Tran-Blaha modified Becke-Johnson potential show that the materials are wide band gap insulators with predominant ionic bonding between M$^+$ (metal) and NO$_3^-$ /ClO$_3^-$ ions and covalent bonding (N-O and Cl-O) within nitrate and chlorate anionic group. From the calculated optical spectra, we observe that electric-dipole transitions are due to nitrate/chlorate group below 20 eV and cationic transitions occur above 20 eV. The calculated reflectivity spectra are consistent with the available experimental spectra.