Modulated structures in the new high- Tc superconducting oxides found in a Bi-Sr-Ca-Cu-O system are examined by high resolution transmission electron microscopy. Strong lattice distortions are induced in the [Bi
2O
2] layers to form “Bi- concentrated”and “Bi-deficient” bands in both 80K phase Bi
2Sr
2CaCu
2Oy and 110K one Bi
2Sr
2Ca
2Cu
3 Oy . These distortion bands are arranged to form body- centered orthorhombic lattices with b
s = 2.6nm which is about 4.8 times of the b parameter of the tetragonal sub-structure. Twinning with twin boundary at the center of Bi
2O
2 layer is also observed in the 80 K phase. The modulated structure in the 20 K phase Bi
2Sr
2CuO
y is, on the other hand, described by the monoclinic structure. Structural relations of various modulated structures are discussed.
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