Determination of critical field anisotropy in metal-oxide compounds from the experimental data for polycrystals

Resistive transitions in magnetic fields are measured and the critical fields are determined for polycrystalline samples of Y1Ba2Cu3O7−δ with different microstructures. It is shown that for ceramic samples with weak bonds for good polycrystals, the R(T) dependence can lead to critical fields characterizing the material of the granules rather than the granular medium. The values of parameters dHc2‖/dT and dHc21/dT, for the Y1Ba2Cu3O7−δ single crystals are determined from a comparison of the experimental data for polycrystals with the results of the theory based on the percolation concept. It is shown that for very strong magnetic fields, the nonuniformity of Tc in the sample does not prevent a correct determination of the anisotropy parameters of a metal-oxide compound. The universal nature of the form of resistive transitions in a magnetic field is discussed for polycrystals of high-temperature superconductors with different microstructures.

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