| Summary: | 碩士 === 國立臺灣師範大學 === 物理學系 === 101 === The recent discovered tetragonal superconductor KxFe2Se2 attracts much attention for its high superconducting transition temperature Tc ~ 32 K. The system can be regarded as inserting alkali metal and alkaline earth atoms between the FeSe layers, which is the iso-structure with Ba1-xKxFe2As2(I4/mmm) and the Tc is enhanced greatly from un-intercalated FeSe (Tc = 8.5 K). Hence, we use the ammonothermal method to intercalate β-Fe1+xSe layer by Ba, trying to enhance the superconducting transition temperature. We used the x = 0.008 tetragonal β-Fe1+xSe as the basic material because of its best performance in the superconducting phase transition. with Tc,onset = 13 K and Tc,zero = 9.5 K between x = 0.005 to 0.02
From neutron powder diffraction pattern of Li0.5(NH3)Fe2Se2, the structure is similar to 122 phase but the the site of the alkali metals and alkaline earths are replaced by NH3(2a) and Li located in (2b) and (4c) site respectively. From XRD pattern of Ba intercalated in tetragonal β-FeSe layer by ammonothermal method, we simulated the structure is Ba0.5(NH3)Fe2Se2.which is Li0.5(NH3)Fe2Se2 type structure. The Ba0.5(NH3)Fe2Se2.is an type II superconductor with high Tc = 39 K. we also derived the μ0Hc1(0 K) ~ 21.1 G and μ0Hc2(0 K) ~ 53.82 T.
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