The mean grain size of sintered YBaCuO samples is varied by means of different reaction temperatures. By this procedure, samples having similar densities and mean grain sizes ranging from 4 μm up to 14 μm are obtained. X-ray diffraction patterns show high-quality YBaCuO samples having the same oxygen stoichiometry. The effects of high reaction temperatures are discussed. The influence of different grain sizes on the attainable maximal critical current densities is presented in transport current measurements. It is shown that a maximum current carrying capacity is achieved if the mean grain size, 〈rg〉, approximately equals the Josephson penetration depth, λj (T).
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