YBa_2Cu_3O_<7-δ>の微小組成変化が電気的,化学的性質に及ぼす影響

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In this study, several samples with slight deviations from the metal ion stoichiometry of YBa_2Cu_3O_<7-δ> were synthesized at temperatures from 935° to 980℃. The extent of the single-phase region of the superconducting phase YBa_2Cu_3O_<7-δ>, and the effects of variation in composition on the electrical and the chemical properties were investigated. X- ray diffraction studies of samples with up to 10 at% excess or 1 at% deficit of Cu, and 1.5 at% excess or 5 at% deficit of Ba showed only the YBa_2Cu_3O_<7-δ> phase. The results of DTA measurements and resistivity measurements, however, demonstrated that solid solubility in YBa_2Cu_3O_<7-δ> was very limited : less than 0.5 at% excess or deficit of Cu or Ba could be incorporated. Samples deviating from YBa_2Cu_3O_<7-δ> stoichiometry differed sharply from stoichiometric material in their electrical behavior. Tailing or two step superconductive transitions were found, as well as decreased T_<c end>. Composition variations affected sintering and grain growth. Sintered Cu-poor pellets were porous, having densities 60% or less of theoretical. For Cu- rich and Y- rich-Ba-poor pellets, densities about 90% of theoretical were obtained, and extensive grain growth was observed.
社団法人日本セラミックス協会の論文
1988-04-01