Optimizing the oxygen balance by changing the A-site cations in molecular perovskite high-energetic materials

Abstract

We presented two new members of molecular perovskite high-energetic materials, (H₂pz)[Na(ClO₄)₃] (PAP-1) and (H₂dabco-O)[K(ClO₄)₃] (DAP-O2), in which H₂pz²⁺ (piperazine-1,4-diium) and H₂dabco-O²⁺ (1-hydroxy-1,4-diazabicyclo[2.2.2]octane-1,4-diium) act as A-site fuel cations, respectively. Compared with their H₂dabco²⁺ analogues, (H₂dabco)[M(ClO₄)₃] (H₂dabco²⁺ = 1,4-diazabicyclo[2.2.2]octane-1,4-diium, M = Na⁺ for DAP-1 and K⁺ for DAP-2, respectively), PAP-1 and DAP-O2 exhibit optimized oxygen balance by employing two strategies to change the A-site cations, i.e., “trimming the C and H atoms” of H₂dabco²⁺ by using H₂pz²⁺ to form PAP-1 and adding an O atom into H₂dabco²⁺ by using H₂dabco-O²⁺ to form DAP-O2, respectively. As suggested by DFT calculations and the K–J equation, the smaller H₂pz²⁺ cation in PAP-1 gives a significantly-optimized oxygen balance from −22.0% to −3.9% and an increased crystal density from 2.02 to 2.07 g cm⁻³, resulting in a better detonation performance for PAP-1. Meanwhile the larger H₂dabco-O²⁺ cation gives a slightly-optimized oxygen balance from −21.3% to −17.1% but a decreased crystal density from 2.04 to 1.98 g cm⁻³, leading to a decreased detonation performance from DAP-2 to DAP-O2. This study demonstrated how to rationally choose the A-site cations in a perovskite structure for modulating the properties of molecular perovskite high-energetic materials, providing important clues for designing more advanced energetic materials for practical use.