Structural and Elemental Analysis of Melt-Processible High-Temperature Superconductors by Surface Science and X-Ray Diffraction Measurements

We report the results of scanning electron microscopy (SEM), microprobe analysis (wavelength dispersive and energy dispersive spectroscopies), secondary-ion mass spectroscopy (SIMS), and x-ray diffraction measurements on a series of melt-processed high critical-temperature superconductors. The superconductors were synthesized through a melt reaction between TbBa ₂Cu₃O_7-x and nonstoichiometric rare-earth Ba-Cu-O oxides. The melt-processed samples are dense, largely void-free superconductors with critical temperatures in the 90-95 K range. Microprobe and SIMS data show the absence of Tb in surfaces of the interiors of samples which had been fractured to expose the interior regions. Comparative microprobe and SEM data are included for conventionally prepared sintered samples. Comparative x-ray diffraction studies are presented which show that the melt-processed samples studied have diffraction patterns nearly identical to those of sintered (rare earth)Ba₂Cu₃O_7-x samples. In two of the three Y-based melt-processed superconductors studied, the compound stoichiometry from microprobe analysis is Y₁Ba₂Cu₃O _7-x. The evidence presented indicates that the TbBa ₂Cu₃O_7-x decomposes during the melt reaction.