Direct Observation of Microscopic Inhomogeneities with Energy-Dispersive Diffraction of Synchrotron-Produced X-rays.

Evidence of structural inhomogeneities in two high-transition-temperature superconductors, YBa(2)Cu(3)O(7-delta) and Nd2-xCexCuO4-y, is presented. When samples were illuminated by highly collimated x-rays produced on a synchrotron wiggler, small changes in the lattice were detected over a spatial scale of 10 micrometers. These changes are interpreted as evidence of variations in the oxygen content in one case and in the cerium content in the other; both affect the superconducting properties. The existence of such structural inhomogeneities brings into question whether exotic experimental results obtained from superconducting materials with high transition temperatures actually reflect intrinsic properties.

Synchrotron X-ray Diffraction from a Microscopic Single Crystal Under Pressure.

Metallic filaments with submicrometer diametere have been fabricated. Standard diffraction techniques with conventional x-ray sources were unsuccessful in identifying the structure of these materials. However, with the use of synchrotron radiation produced on a wiggler beam line, diffraction data were obtained in measurement periods as short as 10 milliseconds. Two cylindrical single crystals of bismuth were studied, each with a diameter of 0.22 +/- 0.02 micrometer. The volume of sample illuminated for these measurements was 0.38 cubic micrometer, less than 0.5 femtoliter. The crystals are grown in glass capillaries, and, because bismuth expands on solidification, they are under a residual hoop stress. The crystallographic data indicate the presence of a linear compressive strain of about 2 percent, which is assumed to be the result of a residual stress of about 2 gigapascals.