High pressure structural, elastic and vibrational properties of green energetic oxidizer ammonium dinitramide

TL;DR

This study provides a comprehensive theoretical analysis of ammonium dinitramide's structural, elastic, vibrational, and detonation properties under high pressure, revealing phase transitions and its potential as a green rocket oxidizer.

Contribution

It offers new insights into the pressure-induced structural and vibrational changes of ADN using advanced dispersion-corrected methods, highlighting its phase transition and energetic performance.

Findings

Discontinuities in structural parameters and elastic constants at 5-6 GPa.

Pressure-dependent IR spectra show shifts indicating hydrogen bond changes.

ADN exhibits high detonation performance compared to other ammonium oxidizers.

Abstract

Ammonium DiNitramide (ADN) is one of the most promising green energetic oxidizers for future rocket propellant formulations. In the present work, we report a detailed theoretical study on structural, elastic, and vibrational properties of the emerging oxidizer under hydrostatic compression using various dispersion correction methods to capture weak intermolecular (van der Waals and hydrogen bonding) interactions. The calculated ground state lattice parameters, axial compressibilities, and equation of state are in good accord with the available experimental results. Strength of intermolecular interactions has been correlated using the calculated compressibility curves and elastic moduli. Apart from this, we also observe discontinuities in the structural parameters and elastic constants as a function of pressure. Pictorial representation and quantification of intermolecular interactions are described by the 3D Hirshfeld surfaces and 2D finger print maps. In addition, the computed infra-red (IR) spectra at ambient pressure reveal that ADN is found to have more hygroscopic nature over Ammonium Perchlorate (AP) due to the presence of strong hydrogen bonding. Pressure dependent IR spectra show blue- and red-shift of bending and stretching frequencies which leads to weakening and strengthening of the hydrogen bonding below and above 5 GPa, respectively. The abrupt changes in the calculated structural, mechanical, and IR spectra suggest that ADN might undergo a first order structural transformation to a high pressure phase around 5-6 GPa. From the predicted detonation properties, ADN is found to have high and low performance characteristics when compared with ammonium based energetic oxidizers and well-known secondary explosives, respectively.