Using standard four-point terminal measurements, the intergranular critical current densities jJc(T, B) of sintered YBa2Cu3O7-δ samples are determined. The dependence of the critical current density on the sample geometry (height h and width b of parallel- epiped samples) is measured systematically for various temperatures (5K ≤ T ≤ 91 K) and low applied external magnetic fields (0 mT ≤ μ0Hext ≤ 10 mT). It is shown that the intergranular critical current density increases on reducing the sample height or width, if no external magnetic field is applied to the sample. The results are discussed using a model assuming the currents flowing in a surface layer of the sample. A reduction of the height or width of the sample changes the circumferences and not the current itself, thus implying an enhancement of the critical current density, jJc(T, B). It is found that the increase of jJc(T, B) on reducing the sample dimensions is limited by the Josephson penetration depth, λJ(T). This penetration depth, λJ(T), turns out to be a very important parameter to reach high intergranular critical current densities in sintered high-Tc superconductors.
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