(a) The O A1g representation, carrying the largest magnitude of all degrees of freedom for the 48f O atoms. (b) Vectors depicting the O A1g mode surrounding a linear O′—Bi—O′ group illustrate how the O atoms move out of the plane in which the modes of the Bi T2u representation act (as illustrated in Fig. 11). While all vectors are illustrated, not all of the atoms shown are spanned by a single irreducible representation (i.e. those related by face centering are included).