Kawashima Kenji, Ishida Shigeyuki, Fujihisa Hiroshi, Gotoh Yoshito, Yoshida Yoshiyuki, Eisaki Hiroshi, Ogino Hiraku, Iyo Akira
IMRA Material R&D Co., Ltd., 2-1 Asahi-machi, Kariya, Aichi, 448-0032, Japan.
National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki, 305-8568, Japan.
Sci Rep. 2018 Nov 14;8(1):16827. doi: 10.1038/s41598-018-34265-2.
We synthesized a Fe-based superconductor (FeSC), (La,Na,K)FeAs, and characterized its superconducting properties. It was found that (La,Na,K)FeAs has a 122-type (ThCrSi-type) structure with a space group I4/mmm (No. 139), identical to (Ba,K)FeAs and (La,Na)FeAs but distinct from so-called 1144-type FeSCs such as CaKFeAs and (La,Na)CsFeAs. The results demonstrate that the formation of the 1144-type phase necessitates the large ionic radius mismatch among the so-called A-site constituent elements of the AFeAs formula. The lattice constants are a = 3.850(1) Å and c = 13.21(1) Å. The La, Na, and K ions occupy the same atomic site of Wyckoff position 1a. Electrical resistivity and magnetic susceptibility show the superconducting transition at 22.5 K. The transition temperature (T) of (La,Na,K)FeAs is comparable with that of 122-type (La,Na)FeAs and 1144-type (La,Na)AFeAs (A = Rb, Cs), while being more than 10 K lower than those of typical 122- and 1144-type FeSCs. The results suggest that the random distribution of La and Na ions is the main reason for lower T in the AE = (La,Na) 122-type and 1144-type FeSCs.
我们合成了一种铁基超导体（FeSC），即(La,Na,K)FeAs，并对其超导性能进行了表征。结果发现，(La,Na,K)FeAs具有122型（ThCrSi型）结构，空间群为I4/mmm（编号139），与(Ba,K)FeAs和(La,Na)FeAs相同，但与所谓的1144型FeSC（如CaKFeAs和(La,Na)CsFeAs）不同。结果表明，1144型相的形成需要AFeAs化学式中所谓A位组成元素之间存在较大的离子半径不匹配。晶格常数为a = 3.850(1) Å和c = 13.21(1) Å。La、Na和K离子占据Wyckoff位置1a的同一原子位点。电阻率和磁化率显示在22.5 K出现超导转变。(La,Na,K)FeAs的转变温度（T）与122型(La,Na)FeAs和1144型(La,Na)AFeAs（A = Rb、Cs）相当，但比典型的122型和1144型FeSC低10 K以上。结果表明，La和Na离子的随机分布是AE = (La,Na) 122型和1144型FeSC中T较低的主要原因。
