This important class of metallic structures includes metals such as Co, Zn, Ti & Ru.
The Miller Index notation used to describe the orientation of surface planes for all crystallographic systems is slightly more complex in this case since the crystal structure does not lend itself to description using a standard cartesian set of axes- instead the notation is based upon three axes at 120 degrees in the close-packed plane, and one axis (the c-axis) perpendicular to these planes. This leads to a four-digit index structure ; however, since the third of these is redundant it is sometimes left out !
Contributors and Attributions
Roger Nix (Queen Mary, University of London)