In-situ, low-temperature synthesis and properties of polycrystalline Ba0.6K0.4Fe2As2 bulk superconductors

Dec. 1 15:00-15:15

*Shinnosuke Ishibashi1, Pavan Kumar Naik Sugali1,2, Hiraku Ogino1,2, Shigeyuki Ishida2, Kenji Kawashima2,3, Hiroshi Eisaki2, Taichiro Nishio1
Department of Physics, Tokyo University of Science, 1 Chome-3 Kagurazaka, Shinjuku City, Tokyo, 162-8601, Japan1
Research Institute for Advanced Electronics and Photonics, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Central 2 Umezono Tsukuba, Ibaraki, 305-8568, Japan2
IMRA Materials R&D Co. Ltd., Kariya, Aichi 448-0032, Japan3

Since the discovery of iron-based (IBS) superconductors in 2008, research has been conducted intensively on fundamental properties for potential applications. Several families such as REFeAsO, AEFe2As2, AFeAs, AEAFe4As4 (RE = rare earth, AE = alkali or alkali earth, A = alkali metal) etc., were developed in IBS and optimally doped (Ba0.6, K0.4)Fe2As2 (BaK122) is considered to be superior owing to the high superconducting transition temperature and high critical current density. Meanwhile, there are some difficulties in sample preparation such as unwanted reactions of IBS with various dopants limiting their potential applications. In the present work, we address this problem and developed a novel in-situ and low-temperature synthesis method of polycrystalline BaK122 samples by addition of Sn. Studies of x-ray diffraction indicated the phase formation of BaK122 at 500 oC with the 10 wt. % Sn addition and we have successfully reduced the phase formation temperature of about 250 oC. The microstructural features investigated by the scanning electron microscopy indicated the grain sizes of BaK122 synthesized via our low-temperature method are relatively smaller compared to conventionally produced and are about 1.5 ┬Ám. All samples indicated onset of bulk superconductivity up to 37 K. In this presentation we will also address the optimization of synthesis conditions and their influence on the structural, microstructural, composition variations and superconductivity of polycrystalline BaK122 bulks.

Keywords: IBS, Phase formation, Critical tempreture, X-ray diffraction