12) The tilting is described using the symbols a, in which the three letters abc, respectively, refer to the magni tudes of the tilts around the [100], [010], and [001] directions of the aristotype, and the superscript # takes the value 0, {, or | that indicate no tilt around an axis and tilts of successive octahedra in the same and opposite senses, respectively.
Þ2 We use irreducible representations pertaining to the cubic phase, even though the phase we consider is not cubic, but pseudocubic. In our previous study of SrZrO 3 , 13) we noted that the sequence of condensation of soft modes from the hightemperature cubic phase is R 25 , M 3 , and finally R 25 again, on the basis of Ref. 7). Recently, however, Howard et al. 11) pointed out that the space group Cmcm previously proposed really corresponds to Imma. Thus we alter softmode condensation from the cubic phase.