# U parameter in hexagonal unitcells

1. ### sryzdn

7
Hi,

I have encountered in the papers that people present a, c and c/a as the parameters measured for any hexagonal unit cell. But what is u (angstrom) that sometimes appear among the parameters of a hexagonal unit cell?

75
According to http://arxiv.org/abs/1308.1542, the u parameter represents the relative position of two hexagonal close-packed sublattices in the structure (for example, in a binary compound like ZnO).