Thermal decomposition mechanisms and stability of NTO crystal involving molecular vacancy and surface effects: DFTB-MD and DFT studies

3-Nitro-1,2,4-triazole-5-one (NTO) is a potential alternative to TNT, RDX and HMX in high energy density materials (HEDMs) due to its inexpensive synthesis, excellent detonation performance, low impact sensitivity, and high thermal stability, but its underlying thermal decomposition mechanism is ambiguous. In this work, we carry out molecular dynamics simulations based on self-consistent charge density functional tight binding method to study the thermal decomposition mechanism of condensed phase NTO and consider surface and molecular vacancy effects. We observe that the initial decomposition reaction is mainly the rupture of intramolecular chemical bonds, and three primary reaction channels are proposed: cleavage of nitro group (C5 − N5 bond fracture), rupture of C3 − N2 bond in the ring and H atom transfer to carbonyl, in which C5 − N5 bond breaking plays a leading role under high temperature. At molecular vacancy and on surface, we find that the activation barriers of nitro group cleavage and H atoms migration are lower than that in ideal bulk NTO, indicating effective regulations of them on the thermal stability and decomposition reaction kinetics of NTO crystal. The above proposed reaction mechanism and the effects of molecular vacancy and surface are verified from electronic structure calculations and TG-DSC experiment with coarse and fine NTO samples. Our work may shed some light on designing HEDMs with better performance, safety and usability.