Electron micrographs of δ-MnO2 nanoparticles. (a) Intermediate-magnification image of curled particles viewed edge on. The particles contain two–five layers. (b) High-magnification view of a hexagonal crystal folded on one edge and revealing the type of lattice fringes shown in (a). The U-shaped crystallite has a radius of curvature of 14 Å. (c) High-magnification image of hexagonal crystals viewed parallel and perpendicular to the layer plane.