J Supercond Nov Magn https://doi.org/10.1007/s10948-017-4385-x ORIGINAL PAPER Grain Boundary Shortening in CuTl-1234 Superconductor by the Addition of ZnO Nanoparticles M. Usman Muzaffar 1 · Syed Hamza Safeer 1 · Nawazish A. Khan 1 · A. A. Khurram 2 · T. Subhani 3 · Rabia Nazir 4 Received: 4 July 2017 / Accepted: 11 October 2017 © Springer Science+Business Media, LLC 2017 Abstract The superconducting properties of Cu 0.5 Tl 0.5 Ba 2 Ca 3 Cu 4 O 12−x are studied after the inclusion of ZnO nanoparticles. The ZnO nanoparticles prepared by a sol- gel method were incorporated during the second stage of the synthesis of Cu 0.5 Tl 0.5 Ba 2 Ca 3 Cu 4 O 12−x phase in y = 0, 3.0, 5.0, and 7.0 wt%. It is observed that the struc- ture, the morphology, and the superconductivity properties are greatly influenced by the inclusion of ZnO nanoparti- cles. The lattice parameters of the orthorhombic phase of Cu 0.5 Tl 0.5 Ba 2 Ca 3 Cu 4 O 12−x superconductor are decreased with the increase of x . Similarly, the grain morphology has been changed from needle-like to spherical grains. One of the major benefits of the inclusion of ZnO nanoparticles is the increase in critical temperature, critical magnetic fields, and critical current density as observed from the theoretical calculations of fluctuation-induced conductivity analysis. Keywords Superconductor · ZnO nanoparticles · Grain boundaries · Fluctuation · Conductivity  A. A. Khurram khuram qau@yahoo.com 1 Materials Science Laboratory, Department of Physics, Quaid-i-Azam University, Islamabad, Islamic Republic of Pakistan 2 Laboratory for Advance Materials Processing, National Center for Physics, Islamabad, Islamic Republic of Pakistan 3 Department of Materials Science and Engineering, Institute of Space Technology, Islamabad, Islamic Republic of Pakistan 4 PCSIR Laboratories, Applied Chemistry Research Center, Lahore, Islamic Republic of Pakistan 1 Introduction Since after the beginning of the era of nanotechnology, nanoparticles have been found to have many applications as inclusions to modify the electrical, optical, and mechan- ical properties of the matrix in which they are incorpo- rated [1–3]. One of the promising applications of magnetic and insulating nanoparticles in high-T c superconductors is their use as pinning centers to enhance critical current density [4–7]. The fundamental requirement of stopping the fluxons’ motion is the presence of nonsuperconduct- ing defects of the order of coherence length having a comparable spacing [8]. The formation of such controlled defects during synthesis is very difficult [9]. Thanks to nanotechnology which has made the problem easy [4–7]. The nanoparticles in various shapes, sizes, and types are now available to be included in high-T c superconductors to act as flux pinning centers. However, apart from their use as flux pinning centers, another possible application of nanoparticles is to improve the intergrain connectivity of cuprate superconductivity. The disorder at the grain bound- aries in high-T c superconductors is an existing problem since the discovery of superconductivity in cuprate [10]. The poor grain boundaries can suppress the superconduc- tivity by reducing the zero-resistivity critical temperature [11]. The incorporation of either metallic or semiconduct- ing nanoparticles at the grain boundaries can enhance the intergrain tunneling of the Cooper pairs and improve the superconductivity. In the present article, ZnO nanoparticles have been selected to improve the intergrain connectivity of Cu 0.5 Tl 0.5 Ba 2 Ca 3 Cu 4 O 12−x (Cu 0.5 Tl 0.5 -1234) supercon- ductor. ZnO nanoparticles have very high melting point (1975 ◦ C) and, therefore, during the synthesis of the sam- ples at elevated temperature (around 850 ◦ C), would not consume ZnO particles.