THE MODULATION OF THE MONOCLINIC BI2SR2CUO6+DELTA PHASE

A polycrystalline sample of the monoclinic phase Bi2Sr2CuO6 has been prepared. The displacive modulation, also present in other compounds of the Bi-Sr-Ca-Cu-O system, has been investigated by means of both electron diffraction and electron microscopy. The modulation is commensurate but it is affected by a strong instability. Discommensurations produce an incommensurate modulation that, in our sample, does not have a well ordered periodicity; this is likely due to a partial disorder of the excess oxygen atoms. A higher-order superstructure (eightfold), also found in the same preparation, is also affected by discommensurations. © 1992 Academic Press, Inc.