Observations of long-period structures associated with charge ordering in ${\mathrm{Bi}}_{0.2}$${\mathrm{Ca}}_{0.8}$${\mathrm{MnO}}_3$

Long-period structures with 32- and 36-fold periodicity to the original unit lattice distance were observed in a perovskite manganese oxide ${\mathrm{Bi}}_{0.2}$ ${\mathrm{Ca}}_{0.8}$ ${\mathrm{MnO}}_3$ at around 130 K, in addition to the one with fourfold periodicity. Quantitative electron diffraction profiles were measured for the long-period structure, where the intensity of superlattice reflections was observed to increase with increasing scattering angle due to static strain. This result gave a reasonable explanation for occurrence of the charge ordering of ${\mathrm{Mn}}^{3+}$ and ${\mathrm{Mn}}^{4+}$ ions, which was responsible for the creation of the long-period structures in ${\mathrm{Bi}}_{0.2}$ ${\mathrm{Ca}}_{0.8}$ ${\mathrm{MnO}}_3$.