IN SEARCH OF LOW-TEMPERATURE STRUCTURAL-CHANGES IN BI2SR2CACU2OY - AN X-RAY-DIFFRACTION STUDY

The atomic structure of the Bi2Sr2Can-1CunOy high-T-c superconductors is distinguished by incommensurate modulations, but their implications for superconductivity are as yet uncertain. Recent studies have suggested a strong invlovement due to the modification of the Cu site environment, and a strong electron lattice interaction would be expected to produce distinct structural changes in the vicinity of T-c. This paper presents the first detailed study of the temperature response of the incommensurate modulation in a high quality single crystal of Bi2Sr2CaCu2Oy. The x-ray scattering measurements show no evidence of any changes in either the period or the amplitude of the modulation over the temperature range studied (T=200-18K). The results limit any possible structural involvement to distortions with a local ordering of less than 100 Angstrom in size. A very small but reproducible decrease in the intensity of Bragg and satellite reflections was noted at similar to 140-120K which is suggestive of a minor change in electron distribution.