New critical-state model for critical currents in ceramic high-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>T</mml:mi></mml:mrow><mml:mrow><mml:mi>c</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>superconductors

Critical-current and magnetization measurements are performed on a large number of ceramic superconductors of the Y${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ family. The results show that critical currents in present ceramics depend strongly on sample geometry and are, in fact, completely determined by self-field limitation. The strong magnetic field dependence leads to a general relation between critical current and magnetization which is experimentally found to be satisfied. A quantitative critical-state model based on an extension of Bean's theory is outlined which is able to predict transport and magnetic properties using microscopic current vs magnetic field relations. The underlying microscopic parameters are extracted from a comparison of the model calculation with measured transport and magnetization data.

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