A new aspect of the structural modulation in crystal Bi2Sr2CaCu2Oy

Scans by means of x-ray diffraction of both the fundamental and the modulation-related reflections in the b*c* reciprocal plane were carried out for a highly oriented Bi2Sr2CaCu2Oy crystal with sufficiently small intrinsic mosaicity. In addition to the satellites, modulation-related additional reflections which are incompatible with the generally accepted Bbmb symmetry were recorded for up to the second order. For the first time, it was found that, for this high-quality single crystal, the position distribution of the modulation-related reflections arranged around each fundamental reflection could not be translated between the 00l (l even, from two to 30) and the 0k0 (k even, from zero to six) Bragg reflections, if the weak additional reflections were taken into account. We suggest that there may exist different extinction rules on the b* and c* axes for the modulation-related additional reflections. (author)