Zheng Lu, Miao Xiao, Sakai Yusuke, Izumi Masanari, Goto Hidenori, Nishiyama Saki, Uesugi Eri, Kasahara Yuichi, Iwasa Yoshihiro, Kubozono Yoshihiro
Research Laboratory for Surface Science, Okayama University, Okayama 700-8530, Japan.
Department of Applied physics, The University of Tokyo, Tokyo 113-8564, Japan.
Sci Rep. 2015 Aug 4;5:12774. doi: 10.1038/srep12774.
We previously discovered multiple superconducting phases in the ammoniated Na-doped FeSe material, (NH3)yNaxFeSe. To clarify the origin of the multiple superconducting phases, the variation of Tc was fully investigated as a function of x in (NH3)yNaxFeSe. The 32 K superconducting phase is mainly produced in the low-x region below 0.4, while only a single phase is observed at x = 1.1, with Tc = 45 K, showing that the Tc depends significantly on x, but it changes discontinuously with x. The crystal structure of (NH3)yNaxFeSe does not change as x increases up to 1.1, i.e., the space group of I4/mmm. The lattice constants, a and c, of the low-Tc phase (Tc = 32.5 K) are 3.9120(9) and 14.145(8) Å, respectively, while a = 3.8266(7) Å and c = 17.565(9) Å for the high-Tc phase (~46 K). The c increases in the high Tc phase, implying that the Tc is directly related to c. In (NH3)yLixFeSe material, the Tc varies continuously within the range of 39 to 44 K with changing x. Thus, the behavior of Tc is different from that of (NH3)yNaxFeSe. The difference may be due to the difference in the sites that the Na and Li occupy.
我们之前在氨化钠掺杂的FeSe材料(NH3)yNaxFeSe中发现了多个超导相。为了阐明多个超导相的起源，我们全面研究了(NH3)yNaxFeSe中Tc随x的变化情况。32K的超导相主要在x低于0.4的低x区域产生，而在x = 1.1时只观察到一个单相，其Tc = 45K，这表明Tc显著依赖于x，但随x的变化是不连续的。随着x增加到1.1，(NH3)yNaxFeSe的晶体结构不变，即空间群为I4/mmm。低Tc相（Tc = 32.5K）的晶格常数a和c分别为3.9120(9) Å和14.145(8) Å，而高Tc相（~46K）的a = 3.8266(7) Å，c = 17.565(9) Å。在高Tc相中c增大，这意味着Tc与c直接相关。在(NH3)yLixFeSe材料中，随着x变化，Tc在39到44K范围内连续变化。因此，Tc的行为与(NH3)yNaxFeSe不同。这种差异可能是由于Na和Li占据的位点不同所致。
