The effect of silver doping on the microstructure and transport properties of the YBCO bulk system have been investigated through scanning electron microscopy observation, resistivity and susceptibility measurements, including the critical current density. We have used the additive method for the YBCO system (0.01-60 wt% of Ag). The results of the structural and superconductivity properties show that silver doping has no noticeable effect on the T c of samples, but influences the samples' J c , which increases with increasing silver doping content up to 20 wt% for the YBCO system. The intergranular T c (detected by the imaginary parts of the susceptibility) improved in the doped samples up to the 20 wt% Ag. It was found that excess metallic Ag filled the pores of the bulks and encouraged the formation of larger stacks of flat rectangular platelets, resulting in a c-axis preferred orientation.

The contrast of dislocations in X‐ray topographs taken in the Guinier–Tennevin mode with synchrotron radiation has been studied. In reflections where high orders were insignificant, dislocation images appeared very similar to those in Lang topographs taken with characteristic radiation. At large specimen‐to‐plate distances orientation contrast is important in the direct image. The sense of the Burgers vector of dislocations showing double contrast can be deduced.

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