Perovskite energetic materials (PEMs) have emerged as an attractive class of high-energy-density materials because their modular ABX₃ framework allows independent regulation of the organic A-site cation, inorganic B-site cation, and energetic X-site anion. In particular, modifying the A-site cation provides an effective route for controlling crystal structure, thermal stability, and mechanical response. However, achieving simultaneously high thermal resistance and appropriate mechanical safety remains a major challenge in the development of advanced energetic materials.
In a recent study published in Energetic Materials Frontiers , researchers from Northwestern Polytechnical University in Xi’an, China, introduced a second methyl group into the A-site cation of the established DAP-4 perovskite framework and successfully synthesized the dimethyl-substituted material DAP-DM4. The resulting molecular modification not only substantially enhanced thermal stability but also triggered an unexpected dimensional transformation from a three-dimensional (3D) perovskite structure to a one-dimensional (1D) chain architecture.
Double Methylation Drives a 3D-to-1D Structural Transformation
Single-crystal X-ray diffraction shows that DAP-DM4 adopts a markedly different structure from both its parent compound DAP-4 and the monomethylated derivative DAP-M4. While DAP-4 and DAP-M4 retain three-dimensional perovskite frameworks, DAP-DM4 forms an extended one-dimensional chain structure composed of inorganic chains and organic cations arranged alternately.
The structural transformation is closely associated with the increased steric bulk of the dimethylated A-site cation. Hirshfeld analysis shows that the molecular volume of the dabco-based cation increases from 146.86 ų in DAP-4 to 172.03 ų after monomethylation and reaches 200.86 ų after dimethylation. The enlarged organic cation introduces substantial steric repulsion into the lattice, disrupting the highly symmetrical 3D perovskite framework and driving the crystal toward a 1D chain architecture.
N–H Passivation Dramatically Enhances Thermal Stability
The most significant consequence of dimethyl substitution is the complete removal of labile N–H bonds from the A-site cation. These N–H groups were associated with vulnerable sites that can initiate decomposition in conventional DAP-4 and DAP-M4. Thermal analysis showed that DAP-DM4 exhibited an onset decomposition temperature of 373.5 °C, approximately 15.1 °C higher than DAP-4 and 9.8 °C higher than DAP-M4. This value ranked among the highest reported for perovskite energetic materials and was attributed primarily to the dimethyl passivation of labile N–H sites. By eliminating these vulnerable proton sites, the molecular framework achieves substantially enhanced resistance to thermal decomposition.
One-Dimensional Chains Promote Interchain Energy Dissipation
The dimensional transformation had a pronounced effect on mechanical response. Hirshfeld surface analysis revealed that increasing methylation progressively suppresses strong H···O/O···H hydrogen-bonding interactions while increasing weaker H···H van der Waals contacts. In DAP-DM4, the complete removal of N–H hydrogen-bond donors prevented the formation of an extensive three-dimensional hydrogen-bond network.
The resulting weaker interchain cohesion allowed the one-dimensional chains to slide relative to one another under friction, thereby dissipating mechanical energy and reducing friction sensitivity. DAP-DM4 exhibits a friction sensitivity of 54 N, substantially improved compared with the corresponding monomethylated and unmethylated materials.
However, this structural flexibility came with a trade-off. The weakened lattice constraint adversely affected impact resistance, and DAP-DM4 exhibited a relatively high impact sensitivity of 0.75 J. This contrasting mechanical response highlighted the importance of balancing structural flexibility and lattice constraint in the design of energetic materials.
Toward Ultra-Heat-Resistant Energetic Materials
Although the enhanced thermal stability of DAP-DM4 was accompanied by reduced density and lower detonation performance, its exceptional resistance to thermal decomposition makes it particularly attractive for applications where thermal tolerance is more important than maximum energy output. DAP-DM4 has a density of 1.69 g·cm⁻³, a calculated detonation velocity of 8.194 km·s⁻¹, and a detonation pressure of 29.24 GPa.
The material also exhibited good ambient structural stability, with its crystal phase remaining unchanged after two months of storage under ambient conditions. Significant water absorption occurs only at relative humidity above 80%, suggesting reasonable stability during routine handling under normal environmental conditions.
Conclusion
Overall, this study establishes A-site double methylation as an effective molecular-engineering strategy for simultaneously tuning crystal dimensionality and thermal stability in perovskite energetic materials. The discovery of a one-dimensional, ultra-heat-resistant energetic perovskite provides a new direction for the development of heat-resistant energetic materials designed for extreme-temperature environments, including specialized aerospace pyrotechnics, ignition systems, and deep-well petroleum applications.
###
Contact author details:
School of Astronautics, Northwestern Polytechnical University, Xi’an 710129, China
National Key Laboratory of Solid Propulsion, Xi’an, 710129, China
School of Chemistry and Chemical Engineering, Northwestern Polytechnical University, Xi'an 710129, China
qixiujuan@nwpu.edu.cn (Xiu-juan Qi)
xia_honglei@nwpu.edu.cn (Hong-lei Xia)
qinghuazhang@nwpu.edu.cn (Qing-hua Zhang)
The publisher KeAi was established by Elsevier and China Science Publishing & Media Ltd to unfold quality research globally. In 2013, our focus shifted to open access publishing. We now proudly publish more than 200 world-class, open access, English language journals, spanning all scientific disciplines. Many of these are titles we publish in partnership with prestigious societies and academic institutions, such as the National Natural Science Foundation of China (NSFC).
Energetic Materials Frontiers
Construction of one-dimensional ultra heat-resistant perovskite energetic material via dimethyl passivation of labile N–H bonds
The author Qing-hua Zhang is Editorial Board Member for this journal and was not involved in the editorial review or the decision to publish this article. The other authors declare that they have no competing interests.