Journal of Superconductivity and Novel Magnetism https://doi.org/10.1007/s10948-018-4829-y ORIGINAL PAPER AC Susceptibility of BaZrO 3 Nanoparticles Added YBa 2 Cu 3 O 7-δ Superconductor Prepared via Coprecipitation Method Nurhidayah Mohd Hapipi 1 · Soo Kien Chen 1,2 · Abdul Halim Shaari 1,2 · Mohd Mustafa Awang Kechik 1 · Kar Ban Tan 3 · Kean Pah Lim 1 · Oon Jew Lee 4 Received: 4 May 2018 / Accepted: 31 July 2018 © Springer Science+Business Media, LLC, part of Springer Nature 2018 Abstract In this work, magnetic properties of polycrystalline samples YBa 2 Cu 3 O 7−δ added with x mol.% of BaZrO 3 (BZO) nanoparticles (x = 0.0, 1.0, 2.0, 3.0, 5.0, and 7.0) were studied by AC susceptibility (ACS) measurement. The samples were prepared using coprecipitation (COP) method. X-ray diffraction (XRD) results showed that all the samples were composed of Y-123 as the major phase and Y-211 as the secondary phase. XRD peak of BZO was also observed in the samples added with BZO nanoparticles. The intensity of the peak became higher with increasing amount of BZO addition indicating the presence of increased amount of the unreacted nanoparticles in the samples. The refined lattice parameters indicated that all the samples have an orthorhombic crystal structure without the occurrence of orthorhombic-tetragonal phase transformation. Scanning electron microscopy (SEM) images showed that the samples have randomly distributed grains with irregular shape. The average grain size increased from 0.30 μm for the pure sample to 0.50 μm for the BZO addition of 7.0 mol.%. ACS measurement showed a slight decrease of onset critical temperature, T c−onset (< 1 K) with BZO addition. Both phase lock- in temperature, T cj , and coupling peak temperature, T p , remained relatively unchanged for BZO addition up to 3.0 mol.%. Based on the Bean critical state model, the calculated intergranular critical current density, J cm , for the pure sample is 1.88 A/cm 2 at T p = 84.8 K. For the sample added with 7.0 mol.% of BZO, J cm at T p = 83.6 K is 1.95 A/cm 2 . Keywords YBa 2 Cu 3 O 7−δ · BaZrO 3 · Coprecipitation · Superconductivity · AC susceptibility 1 Introduction YBa 2 Cu 3 O 7−δ (Y-123) is the first high-temperature super- conductor (HTS) discovered with critical temperature, T c , above the boiling point of liquid nitrogen [1, 2]. Such dis- covery marked a significant breakthrough in technological applications as Y-123 can be cooled with a much cheaper cost using liquid nitrogen instead of liquid helium in order  Soo Kien Chen chensk@upm.edu.my 1 Department of Physics, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia 2 Institute of Advanced Technology (ITMA), Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia 3 Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia 4 School of Fundamental Science, Universiti Malaysia Terengganu, 21300 Kuala Terengganu, Terengganu, Malaysia to carry a high transport current. Over the years, much effort has been put forward to study HTS with the ultimate aim to improve T c and critical current density, J c . It was found that one way to increase J c is to enhance the pinning force [3–5]. This can be done by introducing pinning centers into Y-123 so as to prevent the flux lines from moving when the super- conductor is carrying electrical current in the presence of external magnetic field. The pinning capability of undoped Y-123 is rather weak as reflected in the rapid decrease of its J c with applied field presumably due to the lack of effec- tive pinning centers [6–8]. Defects and nano-inclusions are among the flux pinning sites [6, 7]. These defects can be induced by addition of nanoparticles into Y-123 leading to the formation of strong artificial pinning centers [9, 10]. BaZrO 3 (BZO) in the form of nanoparticles is a potential dopant for enhancing the pinning of HTS since it does not dope into the Y-123 lattice [11]. Moreover, its high melting point leads to the smaller particles due to the slow kinetic growth [3]. Most importantly, BZO has a large lattice mismatch with Y-123. The strain between the phases produces defects that enhance the pinning strength