The director vector (a, b) describing the direction of the order parameter for the various Cm structures reported for x = 0.48 (see text). Structures that are not consistent with a single three-dimensional order parameter are not included. For comparison, the directors of the Cm structures reported by Yokota et al. (2009) for 0.15 ≤ x ≤ 0.4 are also shown. The special directions corresponding to the rhombohedral, tetragonal and orthorhombic phases are indicated.