Degradation of YBC critical current as a result of annealing in air
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Degradation of YBC critical current as a result of annealing in air Judith Bransky Oranim, Department of Physics, University of Haifa, Tivon, 36910, Israel (Received 2 September 1992; accepted 30 December 1992)
The present study was aimed at determining the rate of degradation of the transport critical current density Jc of ceramic YBCO stored in atmosphere, as a function of temperature. The transport critical current of ring-shaped samples was measured by the inductance technique. The samples were prepared by the standard method. The results show that annealing at 100 °C for over 500 h caused practically no degradation of Jc. Above 100 °C the rate of degradation increases rapidly with temperature.
It has been established that a pronounced degradation of the superconducting properties of ceramic YBa2Cu3O7-g exposed to the atmosphere is caused by humidity.1"5 The objective of the present study was to determine the rate of degradation of the transport critical current density Jc of ceramic YBCO stored in atmosphere, as a function of temperature. Jc, of ringshaped YBC samples, was measured by the inductance technique described elsewhere.6-7 The samples were prepared by the standard method described in detail in an earlier publication.7 The powder was pressed directly into rings by means of a die with a four jaw clamp. Subsequently, the rings were sintered and annealed in oxygen. Pairs of samples were annealed in air with relative humidity (RH) of 40% at various temperatures between 100 °C and 250 °C for different time durations. The critical current was measured in liquid nitrogen. The samples were transferred directly from the annealing oven to the measuring device; after the measurement they were dried in warm air and immediately returned to the oven; the whole procedure did not exceed 5 min. The relative humidity in the laboratory was 40%. It has been reported8 that repeated heat cycles from room temperature to 77 K might cause some degradation of the critical current. A pair of reference samples was kept at room temperature in a desiccator. Their Jc was measured the same number of times at the same intervals as the annealed samples. No change in Jc (within the measuring accuracy ±3%) was observed for these reference samples. The results are presented in Fig. 1. It can be seen that annealing at 100 °C for over 500 h caused practically no degradation of Jc. Above 100 °C the rate of degradation increases rapidly with temperature. J. Mater. Res., Vol. 8, No. 5, May 1993
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time (h) FIG. 1. Effect of annealing on Jc.
The origin of the observed degradation of Jc was not investigated. Degradation due to CO 2 , H 2 O effects, slight microstructural changes, or changes in oxygen content can be invoked. However, this study indicates that the transport critical current of ceramic YBa 2 Cu 3 07_g is essentially unchanged if the samples are kept in dry air and under 100 °C. ACKNOWLEDGMENTS The author wishes to thank Professor B. Fisher fo
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