Abstract
Bismuth oxysulfide samples of composition Bi4−xCaxO4S3(0 <x <1) were synthesized by solid-state reaction method. The samples with x = 0 and 0.25 show superconducting transition with Tc (zero) 3.3 and 3.7 K. The sample with x = 0.5 shows metal-to-semiconductor transition at ∼ 150 K with no significant change in Tc(onset) and no clear Tc(zero). The sample with x = 0.75 is not superconducting and shows a semiconducting behavior below 150 K. The sample with x = 1 showed strong semiconducting behavior below 100 K. These changes are ascribed to the disintegration of superconducting phase into other non-superconducting phases like Bi2S3. The change in structure as a function of Ca doping was analyzed through X-ray diffraction (XRD), transmission electron microscopy (TEM), and field emission scanning electron microscopy (FESEM). The XRD pattern shows increase in intensity of Bi2S3 peaks with increase in Ca doping at the expense of the intensity of peaks corresponding to Bi4O4S3 phase. The analysis of TEM images indicates the existence of monocrystalline Bi2S3 nanoparticles in all the samples. It also indicates the large shrinkage in lattice parameters of Bi2S3 phase. With the increase in Ca doping, the disintegration of superconducting phase is observed from FESEM images. The critical current density increases with Ca doping of x = 0.25. This increment in Jc is attributed to the increase in density of impurity phases which can act as pinning centers. The pinning mechanism follows scaling law with temperature. Kramer fit to the normalized pinning force response with reduced field confirms the presence of both surface and point pinning centers, where grain boundaries can act as surface pinning centers andx impurity phases can act as point pinning centers in these samples.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call