Superstructures and ordering phenomena in ceramic superconductors
- Lawrence Berkeley National Lab., CA (United States)
It is now well established that the phase transformation behavior of YBa{sub 2}Cu{sub 3}O{sub 6+{delta}} is significantly influenced by matrix strain effects, as evidenced by the formation of accommodation twins, the occurrence of diffuse scattering in diffraction patterns, the appearance of tweed contrast in electron micrographs, and the generation of displacive modulation superstructures of tweed contrast in electron micrographs, and the generation of displacive modulation superstructures, all of which have been successfully modeled via simple Monte Carlo simulations. The model is based upon a static lattice formulation with two types of excitations, one of which is a change in oxygen occupancy, and the other a small displacement of both the copper and oxygen sublattices. Results of these simulations show that a displacive {radical}2 x {radical}2 superstructure forms very rapidly in a morphology of finely textured domains, followed by domain growth and a more sharply defined modulation wavelength, ultimately evolving into a strong <110> tweed with 5 nm to 7 nm period. What is new about these findings is the revelation that both the small-scale deformation superstructures and coarser tweed morphologies can result from displacive modulations in ordered YBa{sub 2}Cu{sub 3}O{sub 6+{delta}} and need not be restricted to domain coarsening of the disordered phase. Figures 1 and 2 show a representative image and diffraction pattern for fully-ordered ({delta} = 1) YBa{sub 2}Cu{sub 3}O{sub 6+{delta}} associated with a long-period <110> modulation.
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 468914
- Report Number(s):
- CONF-960877--
- Country of Publication:
- United States
- Language:
- English
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