Investigating stability in shock compressed europium- and cerium-doped cryptomelane K-OMS-2 through post-shock spectroscopy and microscopy

Abstract

Cryptomelane (K-OMS-2) (K(Mn 4+ , Mn 2+ ) 8 O 16 ) is a manganese-oxide mineral that is abundant in soils and rock coatings globally and is gaining importance in materials science and industrial mineralogy. The crystal structure is composed of 2 × 2 octahedra that creates a tunnel space for K + . Low-weight percent (wt%) europium (Eu)-doped, high-wt% Eu-doped, low-wt% cerium (Ce)-doped, and high-wt% Ce-doped cryptomelane were synthesized for dynamic shock compression experiments using laser-driven flyer plates. Powder X-ray diffraction (XRD), high resolution inductively coupled plasma mass spectroscopy (HR-ICP-MS), transmission electron microscopy (TEM), and Raman spectroscopy (RS) were utilized to characterize the materials pre-shock. TEM and RS analysis of post-shocked material found that high-wt% Eu- and high-wt% Ce-cryptomelane were the most resistant to shock, showing the least amount of peak changes in RS and few amorphous regions in TEM. RS and TEM indicate disorder and defects are present in both high-wt% versions, such as changes in Mn–O bond length, wavy lattice fringes, and amorphous regions near the crystal surface. This study concludes that doped cryptomelane is more resistant to shock compression than unmodified cryptomelane. This study supports the previously proposed thixotropic rebound model as the proposed mechanism for cryptomelane’s shock resistance. During the shock wave, the nanoporosity of the material allows for the material to compress as the shock wave passes through the crystals before relaxing into a similar position as the original state. The addition of higher bond strength metals appears to enhance this overall effect. The results provide context for new material applications and future molecular dynamic modeling.

Bibliographic Information