Response of YBCO superconductor doped with strontium after gamma irradiation

Radiat. Phys. Chem. Vol. 47, No. 5, pp. 691-694, 1996 Copyright © 1996 Published by ElsevierScienceLtd 0969-806X(95)00170-0 Printed in Great Britain. All rights reserved 0969-806X/96 $15.00+ 0.00

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RESPONSE OF YBCO S U P E R C O N D U C T O R D O P E D WITH STRONTIUM AFTER GAMMA IRRADIATION M. M. E L K H O L Y , I L. M. S H A R A F E L - D E E N , t M. M. E L - Z A I D I A , I A. A. E L - H A M A L A W Y 2 and W. M. H U S S A I N 2 ~Physics Department, Faculty of Science, Menoufia University, Shebin El-Kom, Menoufia, Egypt and 2Faculty of Engineering, Menoufia University, Menouf, Menoufia, Egypt Abstract--Different compounds of Y~ Ba2 rSrxCu307_ ~ have been prepared in order to investigate the effect of ,/-irradiation and Sr substitution for Ba on the structure and physical properties of this superconductive system. X-ray measurements show that the samples with different Sr ratios were found to exhibit a single or nearly single superconducting 123 orthorhombic phase before irradiation, and exhibit multiphases after irradiations. The studied samples have the tendency to transform from orthorhombic to tetragonal structures with increasing Sr content. Also an overall slight reduction of the lattice parameters a, b and c is observed by the increasing of Sr content before and after irradiation. From a.c. magnetic susceptibility measurements, for the non-irradiated samples with different Sr contents, transitions with onset temperatures around 83 K were observed and the transition temperatures were found to decrease with increasing Sr content. After irradiation, an overall reduction of the Meissner volume fractions, and a further decrease in the transition temperatures were observed. The effect of different gamma doses on the sample with x = 0.2 was found to suppress the transition temperature and producing of multiphase structures.

INTRODUCTION A few years ago a new class of superconductive materials, which are based on oxygen deficient copper oxides, were discovered (Wu et al., 1987; Takagi et al., 1987). A representative member of these materials which collectively exhibit superconductive transition-temperatures near 90 K is the compound YBa2Cu307_~ which is of great interest from the standpoints of both basic science and potential applications. Those discoveries were soon followed by a much higher critical temperature superconductor T1BaCaCuO, which was discovered (Sheng and Herman, 1988; Shang, 1988) above 120 K. Surprisingly enough, relatively little work was done to study the effect of radiation (Bohandy, 1987; Clark, 1988) on the stability of this class of materials, although it is a highly desirable property of electronic circuit materials to be resistant to high energy ionizing particles and radiations. That is especially important for applications in satellites and other systems operating in the environment of outer space.

EXPERIMENTAL Compounds with the composition Y~ Ba2_xSrxCusO7 ~ (where x = 0.0, 0.1, 0.2, 0.4, 0.6 and 1.0) have been prepared using the solid state reaction technique. Part of the obtained samples were irradiated with a 6°C0 gamma source at room temperature. A v-dose of 10 Mrad was used to study the 691

effect of 7-irradiation on the samples containing different Sr additions. Also, the effect of different y-doses was studied on the sample x = 0.2 with the doses of 10, 20, 30, 40 and 50 Mrad. The temperature dependence of the real part of the a.c. susceptibility X.... was measured using the a.c. inductance technique which is commonly used to measure magnetic susceptibility of superconductors (Sheng and Herman, 1988). For measuring 7, a 1 rms sine wave generator was used at a frequency 1 kHz as our reference source, and an applied field 4.7/~T. Crystal structure study was made by Shimadzu X-ray diffractometer (Model XD-3). Data were analyzed by the Powder Diffraction Package (PDP) (Calligaris, 1990) computer program. RESULTS AND DISCUSSION

1. X-ray studies X-ray diffraction patterns for powdered YBa2_xSrxCu3OT_~, where x = 0.0, 0.1, 0.2, 0.4, 0.6 and 1.0 before irradiation indicate that, the samples exhibit a single or nearly single superconducting 123 orthorhombic phase. For the irradiated samples, we noticed the existence of new diffraction lines which indicate the creation of new nonsuperconducting phases [Y2 BaCuO5 and BaCuO: (Jones et al., 1987)] for all samples. The lattice parameters as well as Miller indices (hkl) for the diffraction lines were calculated by using the PDP program. F r o m these calculations, an overall slight reduction of the lattice

M. M. Elkholy et al.

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parameters a, b and c/3 was observed as a result of Sr substitution which may be attributed to the difference in the ionic radii of Ba and Sr. More reduction of the lattice parameters was observed as a result of irradiating the samples with 7-dose of 10Mrad, which is attributed to the presence of nonsuperconducting phases created by 7-irradiation. Figure 1 shows the X-ray diffraction patterns for the sample with x = 0.2 after being irradiated with different 7-doses (10, 20, 30, 40 and 50 Mrad). It can be seen from this figure that as result of 7-irradiation the degree of splitting of the main orthorhombic peaks at 20 = 32.9 ° and 47 ° are changed and impurity phases (Y2BaCuO5 and BaCuO2) were detected and grew with increasing 7-doses.

the transition temperature is decreased and an overall reduction of the Meissner volume fraction is observed. Also, the existence of multiphase structure which is consistent with X-ray diffraction data is

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2. Magnetic susceptibility The temperature dependence of the magnetic susceptibility (Z) for YBa2_ ~SrxCu307_ ~ with x = 0.0, 0.1, 0.2, 0.4, 0.6 and 1.0 before and after irradiating the samples with 10 Mrad 7-doses showed that for the non-irradiated sample, a sharp transition (AT = 2 K, where AT is the transition width) with an onset temperature around 83 K is observed which indicates a good homogeneity of the sample. After irradiation,

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YBCO superconductor 105

by La (Cava et al., 1988) caused a broadening of the transition and a reduction of Meissner volume fraction. Considering the very short coherence length of these materials, such a random potential may act as a barrier for superconductivity. This may be the reason why the volume fraction decreases with increasing of Sr content. Figure 3 shows the variation of the magnetic susceptibility (X) with temperature for the sample x = 0.2 before and after being irradiated with 10, 20, 30, 40 and 50 Mrad 7-doses at room temperature. From this figure, it is clear that the transition widths are changed and the Meissner volume fraction decreases due to ?-irradiation, also impurity phases are detected. The variation of Tc (offset) and Tc (onset) values as a function of 7-doses for this sample is given in Fig. 4. It is obvious that, both Tc'S are decreased with increasing ?-dose. In addition, for ?-doses 40 and 50 Mrad, the Tc (offset) is not detected above liquid nitrogen temperature. The change in the low-temperature part of Z(t) is conditioned by two factors: the critical current density of weak links, and the change in the grain distribution function (Grishin et al., 1991; Artemov et al., 1990). Since the energy of gamma rays is not sufficient to produce a redistribution of grains, the change in the transition width may be attributed to the decrease in the critical current density of weak links.

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recorded. Also, the Tc (offset) values at which the material turned to diamagnetic values are decreased (Fig. 2) with increasing Sr content for both non-irradiated and irradiated samples. This suppression may be as a result of oxygen deficiency which increased with increasing of Sr substitution (Veal et al., 1987). This suppression is always accompanied by weakening of superconductivity. Similar observations in Y-Ba-Cu-O system were found where either substitution of Y by Ca (Manthiram et al., 1988) or Ba

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M. M. Elkholy et al.

694 REFERENCES

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