In the example shown here, the oxygens located in the face-centers of the perovskite unit cell undergo a slight rotation about the icosohedral axis once is less than . This distortion is related to an order parameter . We can write the free energy in terms of this order parameter as , with as a simple approximation. When , the system has a single free energy minimum at , corresponding to the undistorted, high-symmetry case. When the system has two equivalent minima corresponding to the two possible ways the equatorial O's can move. The upper and lower oxygen planes move in opposite directions to preserve the center of mass of the cell.

In the graphics, the rotation angle is exaggerated in order to visualize the distortion.