300 Journal of Alloys and Compounds, 211/212 (1994) 300-304 JALCOM 121 The effect of neutron and y irradiation on YBCO and B(Pb)SCCO high-Tc superconductors M.M. Zein and W.E. Alnaser Department of Physics, College of Science, University of Bahrain, P.O. Box 32038 (Bahrain) Abstract The effect of neutron irradiation on YBCO high-Tc superconductor (Tc=93 K) and the effect of 7 irradiation on B(Pb)SCCO high-Tc superconductor (Tc = 87 K) were studied. Each sample was given successive irradiation for 5, 10, 15, 20 and 30 h. The mechanical loss spectra were recorded between liquid nitrogen and room temperature. In YBCO, the height of the four relaxation peaks observed increases as the neutron dose is increased. The peak heights increase by nearly a factor of two (when comparing neutron irradiation for 30 h with the non-irradiated sample). In B(Pb)SCCO, the peak heights increase by a factor of 1.5 (for 30 h Y irradiation). The peak temperatures in both high-Tc superconductors show almost no change as a function of the neutron or gamma irradiation. In YBCO, the peaks occur at 113, 123, 147 and 243 K, whereas in B(Pb)SCCO, the peaks occur at 87, 112, 128, 170 and 230 K, when measurement is carried out at 10 MHz using the pulse- echo technique (single-ended). I. Introduction Mechanical loss experiments (internal friction) are very sensitive to the structural defects of compounds and their superconductivity. Ultrasonic attenuation also provides information on superconductors, e.g. the change in the longitudinal and shear sound velocity (Av~ and Av~ respectively) in the vicinity of the critical tem- perature Tc, the longitudinal L and shear G moduli, the bulk modulus B and Young's modulus E. These are related as follows [1-3]: L=pvl2; G=pv12; E=G(3L -4G)/(L -G); AB/B = (hVl/V )[2/{1 4 2 2 Iv, )}] where p is the density of the superconductor. Fur- thermore, from the measurement of the mechanical spectra at different frequencies f, we can calculate with good approximation, the bound energy of small bi- polarons 'A (which is believed to be the mechanism responsible for the relaxation peaks in the vicinity of the critical temperature Tc [4, 5]) using the following relation [6] where W is the activation enthalpy for the relaxation process and fo is the attempt frequency. The effect of the grain size on Tc [7, 8] and on the hysteresis behaviour of both velocities (v~ and vs) [9] was detected by ultrasonic attenuation measurement. In this paper, we study the effect of neutron and y irradiation on two high-Tc superconductor compounds, i.e. YlBa2Cu307_x and Bio.sPbo.2SrCaCul.5Oy, by ultra- sonic attenuation measurement at 10 MHz using the pulse-echo technique (single-ended). 2. Experimental procedures The Y1Ba2Cu30 7 (YBCO) samples used in this study were prepared by the standard solid state reaction in the form of pressed ceramic pellets. The critical tem- perature was found to be 90 K. Bio.aPb0.2SrCaCul.sOy (B(Pb)SCCO) was found to have Tc = 87 K. A detailed explanation of the preparation of YBCO and B(Pb)SCCO and the technique used, i.e. ultrasonic attenuation (at 10 MHz), is given in refs. 10 and 11 respectively. The YBCO high-temperature compound was given successive neutron doses (expressed in units neu- tron-velocity-time, nvt) at room temperature, i.e. 1.8×101° nvt (5 h exposure), 3.6×10 l° nvt (10 h ex- posure), 5.4x 101° nvt (15 h exposure), 7.2x 101° nvt (20 h exposure) and 10.8x 10I° nvt (30 h exposure). The B(Pb)SCCO high-temperature superconductor was irradiated by y rays (expressed in units gamma par- ticles-velocity-time, yvt) giving doses of 4.28 x 108 yvt (10 h exposure), 6.45 x 108 yvt (15 h exposure), 8.6 x l0 s yvt (20 h exposure) and 12.85 x 108 yet (30 h exposure). 0925-8388/94/$07.00 © 1994 Elsevier Science S.A. All rights reserved SSD! 0925-8388(94)00121-R