Application of Synchrotron Powder X-ray Diffraction to Structural Studies of High-Tc Systems. D. E. Cox, Physics Department, Brookhaven National Laboratory, Upton, NY 11973.
Synchrotron x-ray powder diffraction techniques have proved to be very valuable for the structural characterization of many high-Tc superconductors and related systems. Because of the excellent instrumental resolution and peak-to-background discrimination, many subtle features may be revealed, such as weak impurity peaks, small lattice distortions, and anisotropic broadening of neighboring peaks indicative of size and strain effects. The high degree of preferred orientation exhibited by flat-plate specimens of many of these materials can be avoided by the use of capillary samples and suitably short wavelengths (0.5-0.7Å), and the high quality of data collected in this way allows even light-atom positions to be determined with quite good accuracy. In addition, resonant scattering techniques can be used as a probe of cation distribution for most of the constituent elements of high-Tc superconductors. Some examples will be given of recent structural studies of these systems, involving a complex multiphase system, the application of resonant scattering techniques, and phase transition studies at high pressures and low temperatures in a diamond-anvil cell.
This work was supported by the US Department of Energy, Division of Materials Sciences, under contract no. DE-AC02-76CH00016.