Structural changes of long-period modulated structure (LPMS) of the Bi2Sr2(Ca1-xNdx) Cu2Oa + δ ceramics with x are investigated by means of electron diffraction. Increasing x, the modulation mode of the mixing of domains of two modulation periods with b=4.5bo and b=5bo changes to that with b=4.5bo and b=4bo through the modulation mode with only b=4.5bo at x=0.4-0.5. The wavenumber of the superlattice reflection shows a stepwise increase rather than a linear increase with x. Excess oxygen in a LPMS model with the site of excess oxygen is shown to be consistent with excess oxygen analyzed chemically by iodometry and its change with x.
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