bling of the unit cell in the tilt plane (as the rotations of adjacent octahedra within the plane have opposite senses), but adjacent layers need not tilt with the same sense. The two highest symmetry octahedral tilting modes are: all layers being in phase, a + in the Glazer tilt notation and [C] in the notation of Peel et al. which transforms as a M + 2 distortion mode, and each layer alternating in its sense rotation, a -, [CA] and R - 5 . In 3, the tilts normal to the b and c axes repeat after six and four layers (respectively) and are therefore complex. In total, the tilt sequence for this perovskite is Glazer), where both notations are shown for clarity.