Li Huan, Wang Yanan, Yang Xiaofan, Taguchi Tomoya, Zhi Lei, Goto Hidenori, Eguchi Ritsuko, Ishii Hirofumi, Liao Yen-Fa, Kubozono Yoshihiro
Research Institute for Interdisciplinary Science, Okayama University, Okayama 700-8530, Japan.
National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan.
J Phys Condens Matter. 2020 Jun 23;32(39). doi: 10.1088/1361-648X/ab9911.
We synthesized the alkaline-earth metal-doped FeSe compounds (NH)AEFeSe (AE: Ca, Sr and Ba), using the liquid NHtechnique, to determine their superconducting properties and crystal structures. Multiple superconducting phases were obtained in each sample of (NH)CaFeSe and (NH)BaFeSe, which showed two superconducting transition temperatures ('s) as high as 37-39 K and 47-48 K at ambient pressure, hereinafter referred to as the 'low-phase' and 'high-phase', respectively. The high-phases in (NH)CaFeSe and (NH)BaFeSe were metastable, and rapidly converted to their low-phases. However,values of 38.4 K and 35.6 K were recorded for (NH)SrFeSe, which displayed different behavior than (NH)CaFeSe and (NH)BaFeSe. The Le Bail fitting of x-ray diffraction (XRD) patterns provided lattice constants of= 16.899(1) Å and= 16.8630(8) Å for the low-phases of (NH)CaFeSe and (NH)BaFeSe, respectively. The lattice constants of their high-phases could not be determined due to the disappearance of the highphase within a few days. The XRD pattern for (NH)SrFeSe indicated the coexistence of two phases with= 16.899(3) Å and= 15.895(4) Å. The former value ofin (NH)SrFeSe is almost the same as those of the low-phases in (NH)CaFeSe and (NH)BaFeSe. Therefore, the phase with= 16.899(3) Å in (NH)SrFeSe must correspond to the superconducting phase with theof 38.4 K, while the superconducting phase with= 35.6 K is assigned to the crystal phase with= 15.895(4) Å. For (NH)SrFeSe, a high-phase with= 47-48 K has not yet been obtained, but a new phase showing thevalue of 35.6 K was clearly obtained. This is the first systematic study of the preparation, crystal structure, and superconductivity of alkaline-earth metal-doped FeSe, (NH)AEFeSe.
我们采用液氨技术合成了碱土金属掺杂的FeSe化合物(NH)AEFeSe（AE：Ca、Sr和Ba），以确定其超导性能和晶体结构。在(NH)CaFeSe和(NH)BaFeSe的每个样品中都获得了多个超导相，它们在环境压力下显示出两个高达37 - 39 K和47 - 48 K的超导转变温度（$T_c$），以下分别称为“低相”和“高相”。(NH)CaFeSe和(NH)BaFeSe中的高相是亚稳态的，会迅速转变为低相。然而，(NH)SrFeSe的$T_c$值记录为38.4 K和35.6 K，其表现出与(NH)CaFeSe和(NH)BaFeSe不同的行为。X射线衍射（XRD）图谱的Le Bail拟合分别给出了(NH)CaFeSe和(NH)BaFeSe低相的晶格常数$a = 16.899(1) Å$和$a = 16.8630(8) Å$。由于高相在几天内消失，其高相的晶格常数无法确定。(NH)SrFeSe的XRD图谱表明存在两个相，晶格常数分别为$a = 16.899(3) Å$和$a = 15.895(4) Å$。(NH)SrFeSe中前一个$a$值与(NH)CaFeSe和(NH)BaFeSe低相的值几乎相同。因此，(NH)SrFeSe中$a = 16.899(3) Å$的相必定对应于$T_c$为38.4 K的超导相，而$T_c$为35.6 K的超导相则归属于晶格常数为$a = 15.895(4) Å$的晶相。对于(NH)SrFeSe，尚未获得$T_c$为47 - 48 K的高相，但清楚地获得了一个$T_c$值为35.6 K的新相。这是对碱土金属掺杂的FeSe，即(NH)AEFeSe的制备、晶体结构和超导性的首次系统研究。
