Effect of 120 MeV Oxygen Ion Irradiation on Current-Voltage Characteristics in YBaCuO
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EFFECT OF 120 MeV OXYGEN ION IRRADIATION ON CURRENT-VOLTAGE CHARACTERISTICS IN YBaCuO
A. IWASE*, N. MASAKI*, T. IWATA* AND T.NIHIRA** *Japan Atomic Energy Research Institute, Dept. of Physics, Tokai-Mura, Naka-Gun, Ibaraki, 319-11, Japan **Ibaraki University, Faculty of Engineering, Hitachi, Ibaraki, 316, Japan
ABSTRACT The effect of 120 MeV oxygen ion irradiation on the current-voltage(I-V) characteristics has been studied at 77.3 K in YBaCuO superconductors. In the small current region, the voltage V against the current I and the ion-fluence P can be described by the following simple form; ln(V/V 0 )=aln(I/I 0 )xln(D/%0), where a, V0 ,I discussed in pairs.
0
and D0 are constants.
The experimental results have been
terms of current-induced unbinding of thermally excited vortex
INTRODUCTION One of the remarkable features of the oxide superconductors is the twodimensionality which results from the layered structure of conductive planes. It is well believed that the power law behavior of I-V characteristics near the transition temperature is one of the two-dimensional properties in oxide superconductors, and can be explained as a result of current-induced unbinding of the thermally excited vortex pairs[l-31. This paper reports an experimental study of the influence of the high energy ion irradiation on the non-Ohmic I-V characteristics in YBaCuO at 77.3 K, and shows that the ion-irradiation enhances the dissociation of the vortex pairs[4]. EXPERIMENTAL PROCEDURES Polycrystalline YBa 2 Cu307x samples were formed from aqueous solution of Y-, Ba- and Cu-nitrate in their appropriate ratio. The preparation process is described full in detail in Ref. 4. Since the X-ray pattern of the sample prior to irradiation has strong (00n) (n=l,2,----) peaks(see Fig. 1), the caxis of the sample is strongly oriented perpendicular to the sample plane. Electrical resistance measurements were made by a standard four-probe method. The current was applied perpendicular to the oriented axis. In the present experiment, we used two samples with different T c(R=0). In Fig. 2, the electrical resistance of these two samples is plotted as a function of temperature. One of the samples attained zero resistance at 83 K(sample A), and the other at 89 K(sample B). Irradiations were performed at the JAERI (Japan Atomic Energy Research Institute) tandem accelerator with 120 MeV oxygen ions. The projected range of ions is about the same as the sample thickness of I4O.imm. During irradiations, the temperature of the samples were held below 80 K. The I-V characteristics were measured at 77.3 K for various ion fluences. We note here that all the measurements were performed in zero applied magnetic field.
Mat. Res. Soc. Symp. Proc. Vol. 209. 01991 Materials Research Society
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2e (degree ) Fig.
1 CuKa X-ray diffraction patter for YBaCuO sample prior to irradiation.
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Fig. 2 Temperature dependence of e
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