Density Functional Theory Analysis Identifying the Mechanism for Ignition Sensitivity of Ammonium Periodate Compared with Ammonium Perchlorate

The ignition sensitivity of ammonium perchlorate (APC) and ammonium periodate (API) was analyzed in terms of crystalline structure, thermal and mechanical properties, and electronic structure using density functional theory (DFT) calculations. API is more rigid, with a higher bulk modulus (K) of 25.87 GPa compared with 21.42 GPa for APC. On the other hand, the shear moduli (G) are similar, 9.75 GPa for API and 9.42 GPa for APC. With higher bulk moduli and similar shear moduli, API will experience more shear than compression in situations such as friction. Also, API presents slightly more lateral deformation than APC, with Poisson's ratio (nu) of 0.333, compared with 0.308 for APC, and contributes to a less consistent deformation in terms of the crystal lattice. A less stable lattice structure will contribute to greater ignition sensitivity of API compared with APC. The electronic density of states (DOS) analysis showed that API also has a more ignition sensitive profile with a band gap of a semiconductor type, Delta g = 2.92 eV, while APC is a typical insulator with a band gap of Delta g = 6.21 eV. The analysis of the electronic structure coupled with overall higher anisotropy (shown by calculated elastic constants) could induce ignition of API in a solid phase, whereas the greater stability of APC results in a multiphase ignition mechanism. Results shown here demonstrate important properties that influence the safe handling and use of energetic materials. The observed similarities in structural, mechanical, and thermodynamic properties of API and APC and the considerably large differences in electronic properties indicate that the latter is the key to the higher ignition sensitivity of API.