Detailed Study of the Phase Diagram of Fe-based Superconductor Ba(Fe1-xCox)2As2 by Super High-Resolution Neutron Diffraction Measurements

International Conference on Strongly Correlated Electron Systems 2014

Ikeuchi, K.^1 ; Sato, M.^1 ; Li, S.^2 ; Toyoda, M.^2 ; Kobayashi, Y.^2 ; Itoh, M.^2 ; Miao, P.^3,4 ; Torii, S.^3 ; Ishikawa, Y.^3 ; Kamiyama, T.^3,4

Research Center for Neutron Science and Technology, Comprehensive Research Organization for Science and Society (CROSS), Ibaraki-Tokai

319-1106, Japan^1

Department of Physics, Nagoya University, Furo-cho, Nagoya

464-8602, Japan^2

Neutron Science Laboratory (KENS), High Energy Accelerator Research Organization (KEK), Ibaraki Tokai

319-1195, Japan^3

Department of Materials Structure Science, School of High Energy Accelerator Science, Graduate University for Advanced Studies (SOKENDAI), 1-1 Oho, Ibaraki, Tsukuba

305-0801, Japan^4

关键词: Bragg reflection;    High resolution;    Neutron diffraction measurements;    Neutron powder diffractometer;    Physical quantities;    Second order transition temperature;    Temperature regions;    Tetragonal phase;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/592/1/012071/pdf
DOI  :  10.1088/1742-6596/592/1/012071

来源: IOP

【 摘 要 】

Temperature (T) dependence of Bragg reflections of Ba(Fe1-xCox)2As2(x = 0, 0.02) have been measured in detail on assembled mm-size crystallites to avoid effects of surface and/or externally induced strains with the high-resolution neutron powder diffractometer, where we have found that the profile width of the (400)O/(040)Oreflections with the orthorhombic indexing begin to increase, as T decreases, at ∼270 K, much higher than the tetragonal (Tet)-orthorhombic (Ort) second order transition temperature TS(-147.5 K) without showing any indication of an phase change above TS. The coexistence of two Ort phases with different orthorhombicity exists in the region of ∼140 K Oreflections are nearly T-independent in the entire temperature region studied here (130 K ≤ T ≤ 350 K). An additional broadening due to the Co-doping is clearly found. We discuss these results in relation to the breakdown of the 4-fold symmetry of static physical quantities found in the electrical resistivity and band splitting of the 3dyzand 3dzxand orbitals and conclude that the disappearance of the 4-fold symmetry even in the macroscopically tetragonal phase can be understood by the existence of orthorhombic domains induced by crystal defects and/or impurities.