FeSe基超导薄膜制备及新材料探索

FeSe-based layered compounds is a family of new nontoxic high temperature superconducting materials, including the tetragonal FeSe and the intercalated AxFe2Se2 series (A = Li-Cs, Ca-Ba, Yb, Eu, NH4Cl). The highest Tc is 46 K, obseviously higher than the McMillan limitation of 40 K, much closer to the 56 K of the FeAs-based superconductors. The relationship of the crystal structure of tetragonal layered FeSe and the KxFe2Se2 implies the potassium in the latter could be deintercalated without destroy the FeSe layer. The deintercalatation of potassium from KxFe2Se2 has been observed in our preliminary experiment. Through controlling the deintercalated process and rate by chosing proper solvent, atmosphere and PH conditions, the pure tetragonal FeSe can be achieved. Solvent including ethanol, acetone, ether, tetrachloromethane and so on will be investigated to control the deintercalatation process..The monodispersed nanocrystalline FeSe precursor solution can be synthesized by controlling potassium deintercalation from KxFe2Se2 in the liquid high-energy ball-milling process at proper solvent. The spin-coating method will be used to fabricate the FeSe film on different substrate such as SiO2, SiC, and Mo etc. Post-processing including annealing and/or selenide will be investigated to obtain the optimized superconducting film..The latest reported NaxFe2Se2 superconductor was synthesized by liquid ammonia method, however, solid-state reaction trials were not succeed up to now. We prepare to explore many method to synthesis the AxFe2Se2 series compounds, such as Li, Na, K, Ca, Sr, NH4Cl intercalated FeSe layered compounds, which may be "metastable" or decompose at high temperature. High-energy mechanical alloying method, polysulfide self-flux low temperature reaction method, ion-exchange method, liquid method and electrochemical methods will be investigated. Design and synthesis of other complicated perovskite unit intercalated FeSe multilayered compounds are also under consideration.

FeSe基层状化合物是一大类新型无毒高温超导材料，主要包含四方相FeSe和碱金属等插层的AxFe2Se2(A = Li－Cs，Ca－Ba，Yb，Eu，NH4Cl)系列，其Tc最高可以达到46K。本申请拟采用将钾插层的KxFe2Se2反向脱钾的方法，通过控制在不同溶剂、气氛和酸碱度等条件下的反应过程与反应速率，制备纳米晶四方相FeSe。利用液相高能球磨及可控脱钾过程来制备分散性良好的纳米晶FeSe前驱体溶液，采用旋涂及后处理等方法制备FeSe超导薄膜。最新报道在液氨法制备的NaxFe2Se2中可以实现46K的超导转变，但固相法尚未成功。本申请拟探索高能球磨方法，多硫化物低温自助熔剂方法，离子交换方法，液相法，电化学方法等不同合成手段制备Li，Na，K，Ca，Sr，NH4Cl，NH3，CH3OH，I2等插层的FeSe层状化合物。探索复杂钙钛矿结构单元插层的多FeSe层状化合物的设计与合成。

通过利用Mg2+和F- 双掺杂LaOBiS2探究结构变化在LaOBiS2中对超导性能的影响。首次发现了Sr4Bi6Se13体系的超导电性，本征的Sr4Bi6Se13呈现金属性行为，不具备超导电性；通过空穴型掺杂的Sr4Bi6.2Se12.8具有2.7K左右的Tc，上临界场Hc2(T)达到29.0kOe。利用磁控溅射法成功制备出FeSe的薄膜，厚度~2.7m，对应的Tc为6.8K左右。在四方相FeS中观察到了转变温度为5 K的超导电性。三维材料SnTe通过In，Se共掺杂SnTe，实现超导转变温度分别为3.1K和3.9K。