Transverse modulation and uniform period in Bi_1-xSr_xMnO₃

The crystal structures of the superstructure phases of the Bi-based manganite Bi_1-xSr_xMnO₃ have been studied by transmission electron microscopy. On the basis of the selected area electron diffraction patterns, our crystallographic analysis revealed that the modulations of Bi_1-xSr_xMnO₃ consist of only transverse modulation associated with the Pcnn-type symmetry, in contrast to the previously believed Ibmm-type symmetry. Moreover, our high-resolution transmission electron microscopy image indicated that a modulation with a noninteger-multiple period has a uniform period but not the mixed state of adjacent integer-multiple periods according to the lever rule.