The distortion of the monoclinic unit cell and the polarization rotation. (a) A schematic showing the monoclinic distortion of the pseudocubic unit cell due to the rotation of the polarization direction. The angle between the polarization vector and the cell-body diagonal is ρ. The unit cell is modelled using four ρ-dependent parameters (c, a, ψ and ξ): c and a are the lengths of the unit-cell edges in and out of the polarization rotation plane, respectively, and ψ and ξ are the unit-cell shear angles. (b) A stereographic projection of polarization rotation planes and directions of polarization P11, P12 and P13 in the monoclinic domains M11, M12 and M13, respectively. An animated version of panel (a) is available in the supporting information.