"Compressional Behavior of Bulk and Nanorod LiMn2O4 under Nonhydrostatic Stress"

Yu Lin: Yuan Yang, Hongwei Ma, Yi Cui, and Wendy L. Mao; J. Phys. Chem. C, 05/04/11.

Additional Authors: Yuan Yang, Hongwei Ma, Yi Cui, and Wendy L. Mao

Abstract:

We studied the effect of pressure on LiMn2O4 commercial powders and well-characterized nanorods using angle-dispersive synchrotron X-ray diffraction (XRD) in diamond anvil cells and found that spinel LiMn2O4 is extremely sensitive to deviatoric stress induced by external applied pressure. Under nonhydrostatic conditions, bulk LiMn2O4 underwent an irreversible phase transformation at pressures as low as 0.4 GPa from a cubic Fd-3m to tetragonal I41/amd structure driven by the Jahn–Teller effect. In contrast, bulk LiMn2O4 under hydrostatic conditions experienced a reversible structural transformation beginning at approximately 11 GPa. Well-characterized LiMn2O4 nanorods with an average diameter of 100–150 nm and an average length of 1–2 μm were investigated under the same experimental conditions and showed a similar structural behavior as the bulk material confirming that LiMn2O4 displays an extremely sensitive structural response to deviatoric stress. Scanning electron microscope (SEM) images of the samples especially the nanorods that were recovered from high pressure demonstrated a link between the changing morphology of the materials and the origin of the phase transition. We also found that nanostructured materials can accommodate more stress compared to their bulk counterparts. Our comparative study of bulk and nanorod LiMn2O4 improves our understanding of their fundamental structural and mechanical properties, which can provide guidance for applied battery technology. In addition, LiMn2O4 represents a strongly correlated system, whose structural, electronic, and magnetic properties at high pressure are of broad interest for fundamental chemistry and condensed matter physics.