Microstructural characterization of GdBa2Cu3O7-δ superconductor films with BaHfO3 artificial pinning centers by scanning transmission electron microscopy

Kazuhiro Yamada; Takeshi Nishiyama; Kenji Kaneko; Yukio Sato; Ryo Teranishi; Takeharu Kato; Akira Ibi; Masateru Yoshizumi; Teruo Izumi; Yuh Shiohara

doi:10.1093/jmicro/dfu082

Microstructural characterization of GdBa2Cu3O7-δ superconductor films with BaHfO3 artificial pinning centers by scanning transmission electron microscopy

Microscopy (Oxf). 2014 Nov:63 Suppl 1:i27-i28. doi: 10.1093/jmicro/dfu082.

Authors

Affiliations

¹ Department of Materials Science and Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.
² Nanostructures Research Laboratory, Japan Fine Ceramics Center, 2-4-1 Mutsuno, Atsuta-ku, Nagoya 456-8587, Japan.
³ HTS Conductor Processing & Power Application Division, International Superconductivity Technology Center, 3-2-1 Sakado, Takatsu-ku, Kawasaki 213-0012, Japan.

PMID: 25359826
DOI: 10.1093/jmicro/dfu082

Abstract

Critical current (IC) of superconductor films under magnetic field is strongly influenced by dispersions and morphologies of artificial pinning centers (APCs) in general [1]. BaHfO3 (BHO) is acknowledged as the best candidates of APCs for REBCO films, which shows utmost thickness dependence and isotropic angular dependence of IC values for REBCO films [2]. Moreover, several researchers have focused on the nanostrains caused by the lattice mismatch at the interface between APCs and REBCO matrix, which are also the source for enhanced vortex pinning of the REBCO films [3]. In this study, we investigated to examine the nanostrain at the interface using spherical aberration (CS) corrected scanning transmission electron microscopy (STEM).BHO introduced GdBa2Cu3O7-δ (GdBCO) film was fabricated by pulsed laser deposition (PLD) method. TEM samples were prepared by focused ion beam (FIB; Quanta 3D 200i, FEI) method followed by Ar ion thinning (NanoMill, Fischione) method. Atomic scale imaging was performed by spherical aberration corrected STEM (JEM-ARM200F, JEOL), then microstructures of BHO/GdBCO interface was then examined by Fourier transformation (FFT).BHO nanorods and nanoparticles were found dispersed in the GdBCO matrix, where {100} and {110} facets were present at BHO/GdBCO interfaces, as shown in Fig. 1. In the case of PLD process, most favorable growth direction of BHO is [001] direction, so that the regular quadrangular prism shaped BHO with {100} facets would be grown along [001] direction of GdBCO matrix [4]. {110} facets of BHO were formed to maintain the minimum surface area at BHO/GdBCO to reduce the interfacial energy.jmicro;63/suppl_1/i27-a/DFU082F1F1DFU082F1Fig. 1.Plan view HAADF-STEM image and FFT image showing facets at BHO/GdBCO interfaces. This work was supported by the Ministry of Economy, Trade and Industry (METI) as "Development of Fundamental Technologies for HTS Coils" and the JSPS KAKENHI (26600046).