Sugali Pavan Kumar Naik, Ishida Shigeyuki, Kimoto Koji, Yanagisawa Keiichi, Kamiya Yoshihisa, Tsuchiya Yoshinori, Kawashima Kenji, Yoshida Yoshiyuki, Iyo Akira, Eisaki Hiroshi, Nishio Taichiro, Ogino Hiraku
Department of Physics, Tokyo University of Science, 1 Chome-3 Kagurazaka, Shinjuku City, Tokyo 162-8601, Japan.
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, Japan.
Phys Chem Chem Phys. 2021 Sep 15;23(35):19827-19833. doi: 10.1039/d1cp02613e.
We investigated the defect structures of polycrystalline CaKFeAs (CaK1144) superconductors by scanning transmission electron microscopy (STEM). The STEM studies revealed the presence of a one-layer CaFeAs (∼1 nm size) defect along the -plane, as observed in single crystalline CaK1144. Step-like CaFeAs defects are also observed. These nanoscale defects generate fine-sized stacking faults, a lattice mismatch, and stress field defects in the matrix of CaK1144 owing to the different sizes. Correlation of the defects in polycrystalline and single crystalline samples suggests that the defects type and their density depend on the synthesis conditions. A self-field critical current density () of 15.2 kA cm was obtained at 5 K, and the curves were sustained above 30 K with a considerable value of 1.4 kA cm. We investigated the relationship between the observed intrinsic defects and the behavior of the field dependence of . The intrinsically intergrown planar defects, even in polycrystalline samples, are expected to be advantageous for various high-field applications of bulk CaK1144 superconductors.
我们通过扫描透射电子显微镜（STEM）研究了多晶CaKFeAs（CaK1144）超导体的缺陷结构。STEM研究表明，在多晶CaK1144中观察到沿c平面存在一层CaFeAs（尺寸约为1 nm）缺陷。还观察到了阶梯状的CaFeAs缺陷。由于尺寸不同，这些纳米级缺陷在CaK1144基体中产生了微小尺寸的堆垛层错、晶格失配和应力场缺陷。多晶和单晶样品中缺陷的相关性表明，缺陷类型及其密度取决于合成条件。在5 K时获得了15.2 kA/cm²的自场临界电流密度（Jc），并且在30 K以上Jc曲线仍然存在，其值相当可观，为1.4 kA/cm²。我们研究了观察到的本征缺陷与Jc的场依赖性行为之间的关系。即使在多晶样品中，本征共生的平面缺陷对于块状CaK1144超导体的各种高场应用也有望具有优势。
