(a) HRTEM images of PD2 with 2 × 2 unit cells, taken along the c axis (Hovmöller et al., 2012). The tenfold wheels with atoms in black are clearly seen. (b) Atomic structure model of PD2 obtained from RED data, projected along the c axis. The circles indicate the 2 nm cluster columns with a pseudo-tenfold rotational symmetry. Ni/Co atoms are in red and Al atoms in blue. (c) Structure model showing the arrangement of Ni/Co atoms at z = 0.25 (red) and z = 0.75 (red with yellow cross) layers. (d) The structure of PD4 (a = 101.3, b = 32.0 and c = 4.1 Å), as determined by X-ray crystallography (Oleynikov et al., 2006). The circles mark the 2 nm clusters similar to those found in PD2. Whole figure reprinted from Singh et al. (2014).