A promising perovskite primary explosive

Primary explosives are essential for precise ignition in commercial, military, and space applications but commonly suffer from toxicity (e.g., heavy metals), complex and hazardous syntheses, instability, and inadequate ignition performance. Transition metal-based initiators involve toxic metals and hazardous precursors; potassium-based systems often require tedious and costly synthesis and can have weak ignition; organic initiators may be unstable and need toxic solvents or risky reactions. To address these issues, the authors propose a green, low-cost, and high-performance initiating explosive based on a double perovskite framework. They design an A2BB'X6 perovskite where periodate (IO4−) serves as the oxidizing X-site anion to balance high ignition performance with acceptable sensitivity, Na+ and NH4+ occupy the B/B' sites to promote compact, biocompatible, water-processable structures, and the A-site is filled by dabconium (H2dabco2+) to maximize density and packing. The target, {(C6H14N2)2[Na(NH4)(IO4)6]}n (DPPE-1), aims to overcome the conventional drawbacks by combining a benign composition with robust stability and strong initiation capability.

Recent years have seen strong interest in perovskite-derived materials due to low-cost solution processing, structural tunability, and functional diversity. Prior energetic perovskites, including silver-based systems such as (H2A)[Ag(ClO4)3], suggested potential as primary explosives but lacked ignition performance data and still relied on heavy, costly noble metals. Reported initiating substances largely feature single-perovskite (ABX3) structures, while double-perovskite energetic materials have not been reported. Periodate-based perovskites offer strong oxidizing capability, potential for three-dimensional frameworks, improved ambient stability, and biocidal iodine as a main decomposition product, but earlier synthesis routes were uneconomical or hazardous and ignition performance required improvement. The literature on potassium-based primaries highlights good performance but often with lengthy, complex syntheses. Overall, the field lacked a green, heavy-metal-free primary explosive with documented high ignition efficiency and robust stability, motivating the present double perovskite design using IO4− and benign cations (Na+, NH4+) with H2dabco2+ as the A-site cation.

Synthesis: DPPE-1 was prepared via a green, one-pot aqueous process at room temperature. Dabconium dihydrochloride (H2dabcoCl2, 2 mmol) and NH4Cl (1 mmol) were dissolved in 5 mL water with vigorous stirring, followed by addition of 8 mL of NaIO4 solution (6 mmol). A white precipitate formed within 2–3 s, which was filtered, washed with ice/water, and dried (yield 72.1%). Characterization: Structure and composition were confirmed by elemental analysis (C, H, N), IR spectroscopy, 1H/13C NMR, powder X-ray diffraction (PXRD), and single-crystal X-ray diffraction (SCXRD). SCXRD established a cubic Pa-3 space group, a = b = c ≈ 14.8 Å, with four formula units per unit cell and high crystal density. Hydrogen bonding networks, packing, and filling coefficient were analyzed. Thermal behavior was assessed by differential scanning calorimetry (DSC) at multiple heating rates. Stability to air, moisture, and light was examined by long-duration exposures with PXRD verification. Long-term storage stability was tested at 75 °C for 48 h. Mechanical sensitivities were measured using standard BAM Fall hammer (impact sensitivity, IS) and BAM friction tester (friction sensitivity, FS). Ignition performance was evaluated via minimum primary charge (MPC) tests using a standardized apparatus comprising an exploder, explosion chamber, and a setup with ignition head, blasting cap, and lead plate, following GJB 5891-2006 protocols. Computational analyses (EXPLO7.0) estimated detonation parameters and detonation product distributions; thermodynamic stability considerations included Gibbs free energy comparisons between IO4−- and ClO4−-based analogs. Decomposition product iodine (I2) was probed experimentally by heating DPPE-1 in sealed vessels and confirming I2 via color changes and starch complexation.

• Composition and structure: DPPE-1 is a double perovskite {(C6H14N2)2[Na(NH4)(IO4)6]}n with H2dabco2+ at the A-site, NH4+ at B, Na+ at B', and IO4− as X. It crystallizes in cubic Pa-3 with a ≈ 14.8 Å and high crystal density (2.89 g cm−3 at 120 K; 2.88 g cm−3 in Table 1). The framework exhibits hierarchical self-assembly with extensive hydrogen bonding and Coulombic interactions and a high filling coefficient (80.7%).
• Stability: Material remained unchanged after 6 months in air, several days in moisture, 2 h direct sunlight, and 30 days sunlight exposure under ambient conditions (PXRD confirmed). Thermal decomposition onset Tdec = 161.3 °C (DSC). Long-term storage test at 75 °C for 48 h showed negligible mass loss (≤0.05%).
• Sensitivity: Impact sensitivity IS = 3.5 J; friction sensitivity FS = 5.0 N, indicating acceptable mechanical sensitivity comparable to many primaries and better FS than lead azide.
• Ignition performance: MPC ≤ 5 mg; DPPE-1 reliably initiated RDX and penetrated lead plates at 20 mg, 10 mg, and 5 mg loadings, demonstrating initiation capability on par with powerful primaries (PbN6, AgN3, CuN6) and superior to reported green primaries such as DDNP, ICM-103, ANTPA, K2DNABT, and K2DNAT.
• Energetics and mechanism: Calculated detonation velocity < 5500 m s−1 and detonation pressure < 18.5 GPa (EXPLO7.0), lower than many primaries, suggesting initiation performance arises mainly from oxidizer behavior and molecular stability rather than bulk detonation metrics. Gibbs free energy comparisons indicate IO4−-based perovskite is less stabilized than its ClO4− analog, correlating with higher sensitivity and initiation efficiency. Oxygen balance is high for a primary explosive (−4.52%).
• Environmental aspects: Heavy-metal-free composition; predicted detonation products are mostly non-toxic or less toxic with I2 as a major solid product (≈51.7% by mass). Experimental heating tests confirmed I2 formation (purple staining and starch test).

The study addresses the long-standing challenge of designing a green, low-cost, and effective primary explosive by leveraging a double perovskite framework with a powerful yet manageable oxidizer (IO4−) and benign cations (Na+, NH4+, H2dabco2+). Despite moderate calculated detonation metrics, DPPE-1 exhibits exceptional initiation performance (MPC ≤ 5 mg), implying that initiation efficiency is governed by oxidizer-driven kinetics and molecular stability within the perovskite lattice. The IO4− anion contributes strong oxidizing capability, and the relative thermodynamic lability of the IO4−-based lattice versus a ClO4− analog likely enhances sensitivity and initiability. The robust three-dimensional framework, dense packing, and extensive hydrogen-bonding network confer environmental and thermal stability sufficient for handling and storage, while the heavy-metal-free design and I2-rich products improve environmental acceptability compared to lead- and mercury-based systems. However, the current thermal decomposition temperature (≈161 °C) suggests limitations for high-temperature applications, indicating that further optimization of perovskite composition may be required to fully supplant legacy primaries like lead azide in all use cases.

DPPE-1, an organic–inorganic double perovskite primary explosive, is synthesized via a simple room-temperature aqueous one-pot method and combines heavy-metal-free composition, good environmental tolerance, acceptable mechanical sensitivities, and ultra-high initiation performance (MPC ≤ 5 mg). Structural analysis reveals a dense cubic Pa-3 lattice with extensive interionic interactions and a high filling factor (80.7%). While its thermal decomposition temperature (161.3 °C) satisfies many requirements, it remains lower than desired for complete replacement of traditional primaries such as lead azide. The work establishes perovskites as a promising platform for green initiating materials and suggests that tuning halogen/oxidizer chemistry and cation selection in double perovskite frameworks could yield future materials with higher heat resistance (Tdec > 200–250 °C) and tailored performance.

• Thermal decomposition temperature is moderate (Tdec ≈ 161.3 °C), below the >200 °C target for robust, high-temperature applications and full replacement of lead azide.
• Calculated detonation velocity and pressure are lower than many established primaries, indicating reliance on oxidizer-driven initiation rather than bulk detonation performance.
• While stability to ambient conditions is good, broader operational envelopes (e.g., prolonged high-temperature or shock environments) and scale-up safety remain to be fully characterized.
• The study focuses on a single composition; generality across other double perovskite chemistries and long-term field performance require further validation.