MODULATED STRUCTURE IN BI2+XSR2-XCU1+YO6+DELTA

The modulated structure in solid solution Bi2+xSr2-xCu1+yO6+delta (0.1 < x < 0.6, y approximately x/4) has been investigated by means of powder x-ray diffraction, electron diffraction, and transmission electron microscopy. The [010] component of the modulation vector decreases almost linearly with increasing x, from 5.2b (x = 0.1) to 4.2b (x = 0.5), where b is the unit length of the average structure along the [010] direction, and is little sensitive to excess oxygen content delta. A structure model of the modulation based on a periodic substitution of Sr for Bi and formation of Bi blocks whose size varies with x is proposed. Relations among various modulations appearing in other related phases such as the Pb-substituted 105 K T(c) phase are discussed.