Comparative study of dimensionality and superconducting parameters in YBCO-NaNbO${}_3$ nanoparticles- and nanorods-added composite sample from excess conductivity analysis

Excess conductivity and dimensional fluctuation effects on the superconducting parameters with the addition of nanoparticles (NPs) or nanorods (NRs) of NaNbO${}_3$ in polycrystalline YBa${}_2$Cu${}_3$O${}_{7-\delta }$ (YBCO) have been studied. Two series of samples were synthesized by solid-state reaction route on addition of 0.5 wt% to 2.0 wt% NaNbO${}_3$ NPs or NRs in pure YBCO superconductor. X-ray diffraction results show the unaffected orthorhombic crystal structure for all the synthesized samples. The field emission scanning electron microscope and high-resolution transmission electron microscope images reflect the addition of NPs or NRs in the YBCO material and indicate that the higher wt% of additive material leads to agglomeration of NPs or NRs. Using the Aslamazov-Larkin model, the fluctuation conductivity and the superconducting parameters such as coherence lengths, critical magnetic fields (B${}_{C1}$(0) and B${}_{C2}$(0)), effective layer thickness (d) and critical current densities (J${}_C$) have been estimated. It has been observed that 0.5 wt% concentration of addition of NaNbO${}_3$ NPs or NRs in YBCO compound shows significant enhancement in B${}_{C1}$(0), B${}_{C2}$(0) and J${}_C$(0), whereas a further increase in additive material results in a decrease in superconducting parameters. In comparison with the pure YBCO, the addition of NPs or NRs is causing a reduction in the magnetic vortex motion that leads to an enhancement in the vortex pinning capability which is responsible for increasing the B${}_{C1}$(0), B${}_{C2}$(0) and J${}_C$(0). Furthermore, a detailed analysis confirmed that the addition of NRs of NaNbO${}_3$ in YBCO is much more effective compared to the NPs for the same wt% of additive material.