The effect of electron irradiation in high- T c oxide superconductors
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The effect of electron irradiation in high-7"c oxide superconductors E. Adem, L. Martinez, J. Rickards, E. Orozco, J. Fuentes-Maya, J. L. Albarran, A. Mendoza, E. Carrillo, L. Cota, J. Reyes-Gasga, J. L. Boldu, R. Perez, J. G. Perez-Ramirez, and J. Jose Yacaman InstitutedeFisica, UniversidadNationalAutonoma de Mexico, ApartadoPostal20-364, Deleg. alvaro obregon, 01000Mexico D. F., Mexico (Received 6 August 1987; accepted 3 June 1988) A superconductor ceramic oxide with the YiBa 2 Cu 3 O 7 _ x phase and exhibiting a transition temperature at Tc ss 92 K, was irradiated at room temperature with 1 MeV electrons. It was found that the irradiation produces a sharp drop in the Tc value from 92 K down to ~ 40 K. The irradiated sample suffered a change from metallike character to semiconductorhke behavior at T> Tc. It is also shown that after irradiation the twin boundaries on the material become irregular.
In the present work we report the effects of electron irradiation on oxide-sintered ceramics with the Y,Ba2Cu3O7 _ x composition, exhibiting superconductivity at Tc =s 92 K as shown in Fig. 1. The samples were prepared by the conventional method reported elsewhere, ' and showed a metallike behavior for temperatures above the superconductivity onset, in agreement with other results previously reported. '~3 The samples were afterwards irradiated in a Van de Graaff electron accelerator at different doses. The beam energy was 1 MeV with a current of 1 0 + 1 //A. The power delivered to the sample was 10 W, which did not produce significant warming of the sample. A thermocouple used to monitor the temperature on the samples during the irradiation indicated minor changes in temperature ( < 20 °C). During the process the irradiation chamber was kept at a pressure of 10~ 6 Torr. The electrical resistance of the parallelepiped-shaped ( 1 0 x 4 x 2 mm 3 ) samples was measured before and after the irradiation. A four-terminal configuration was used. The contacts
were remade after each irradiation. During the measurements, the applied current ranged from 20 to 1 mA for the different samples. At temperatures equal to and below the superconducting transition, care was taken to check that the introduction of small variations in the injected current to the sample did not produce changes in the measured voltage. This procedure assured a reliable superconductor condition. The curves in Figs. 2 (a)
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T(°K) FIG. 1. Resistance versus temperature for a Y 1 Ba 2 Cu 3 O 7m;t superconductor.
J. Mater. Res. 3 (5), Sep/Oct 1988
FIG. 2. Curve of resistance versus temperature for the material in Fig. 1 after electron irradiation at (a) 64 Mrad and (b) 24 krad.
0003-6951 /88/050807-04$01.75
© 1988 Materials Research Society
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radiation up to a dosage of 64 Mrad as shown in Figs. 3(a) and 3(b). However, the irradiated samples presented a large amount of diffuse scattering (Fig. 3). The spot splitting due to the twinning was observed in both ca
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