D. Behera

The effect of swift heavy ion irradiation on critical current density in YB2Cu3O7−δ thick film with Y2O3 addition

The effect of 200 MeV Ag ion irradiation on thick films of YBCO grown by the diffusion reaction technique has been studied. Magnetization at 40 K marks a substantial change in the critical current density (J c) of the irradiated sample when compared with unirradiated ones. The critical current density was estimated from the widths of magnetization loops using Beans critical state model. The enhancement of J c from 1.06×105 to 2.5×105 A/cm2 with irradiation up to a fluence of 5×1011 ions/cm2 in YBCO samples is associated with an increase in the flux pinning created by the irradiation-induced columnar defects. In excess Y2O3 (10 wt%) to YBCO, the J c increases in the pristine sample to 1.33×105 A/cm2 but decreases with increasing fluence. This may be due to an excess of defects, overlapping of defected zones and weakening of the pinning barriers. Further studies using X-ray diffraction and a scanning electron microscope reveal microstructural changes in the irradiated samples.

Effects of SHI irradiation on the critical current density of Y1−x Ca x Ba2Cu3O7−δ thick film with Y2O3 composite

Y1−x Ca x Ba2Cu3O7−δ (x=0.1)+Y2O3 (10 wt%) composite thick film has been prepared by the diffusion reaction technique. Samples are irradiated with 200 MeV Ag ions. X-ray diffraction and scanning electron microscopy reveal microstructural changes in the irradiated samples. The enhancement of the critical current density (J c) from 1.4×104 to 6.7×104 A/cm2 with irradiation in YCaBCO samples is observed, indicating that flux pinning increases due to the creation of columnar defects induced by irradiation. On addition of Y2O3 to YCaBCO, J c increases to 8.3×104 A/cm2. The insulating inclusions of Y2O3 cause J c to increase by the process of flux pinning in the unirradiated YCABCO/Y2O3 composite. However, J c starts decreasing for YCABCO/Y2O3 composite with the increase in ion fluence. The main mechanism of the decrease in the critical current density is the reduction in the effective pinning potential, which is caused by an increase in the defect concentration.

Point Defects Creation by Swift Heavy Ion Irradiation Induced Low Energy Electrons in YBa2Cu3O7−y through Dissociative Recombination

Our in‐situ temperature dependent resistance studies in a set of YBa2Cu3O7−y (YBCO) thin films irradiated with 200 MeV Ag ions at 79 K show that in addition to amorphized latent tracks, a large concentration of point defects are created by the secondary electrons emitted radially from the ion path. Detailed calculation of the energetics indicates that in the YBCO matrix, these secondary electrons cannot create defect by direct elastic knock‐on process. We propose an inelastic interaction of the secondary electrons with the YBCO matrix, which results into defect creation by a process similar to dissociative recombination. Our study shows that accumulation of point defects during irradiation is accompanied by self‐organization of point defect into clustering and phase segregation.

Mesoscopic inhomogeneity creation in YBa2Cu3O7−y thin film by swift heavy ion irradiation at low temperature

In the present study, we report the modification of pulsed laser deposited c-axis oriented thin films of YBa2Cu3O7−y (YBCO) in a cylindrical region around the path of swift heavy ions (SHIs). Our in situ temperature-dependent resistivity measurement and in situ low-temperature X-ray diffraction (XRD) study on YBCO irradiated at liquid nitrogen temperature with 200 MeV Ag ions shows that the SHI-induced secondary electrons selectively create point defects at CuO basal chains of YBCO. Beyond a critical fluence (∼1012 ions/cm2), the radially strained region around the amorphous latent tracks estimated from full width at half-maximum of (00l) XRD peaks tends to overlap, and a two-step superconducting transition evolves instead of a single transition in the in situ resistivity measurement.