Modulation structures of (1) Bi
2+xSr
2-xCuO
z (2201) type of compounds doped with Fe and (2) Bi
2Sr
2CoO
z doped with Pb, are examined by electron diffraction and high-resolution transmission electron microscopy. It is found that modulation periodicity decreases by increase of Bi
3+ and Few replacements of the Cu sites of the 2201 compounds. Modulation periodicity increases by increase of Pb
2+ replacements of the Bi sites in Bi
2Sr
2CoO
z, and finally modulation disappears by 35% or higher replacements. These results are compatible with the expectations based on “excess oxygen model” on the origin of the modulation structures.
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