AN ELECTRON-DIFFRACTION STUDY OF BI2SR2(GDXCA1-X)0.8CU2O8+DELTA

The compound Bi2Sr2(GdxCa1−x)0.8Cu2Oδ is examined by electron diffraction for several values of x. The incommensurate modulation which has been reported for x = 0 persists for all values of x with the wave vector increasing as x increases. A secondary modulation with a wave vector equal to one-half that of the primary is observed for x ≥ 0.85. This modulation manifests itself through satellite reflections that are highly streaked normal to the (001) planes and that flank certain select positions in reciprocal space. The appearance of this secondary modulation is accompanied by a change in the average crystal structure from B-centered to F-centered orthorhombic. © 1990, Materials Research Society. All rights reserved.