以氨熱法形成Ba0.5(NH3)Fe2Se2 的超導性質

Abstract

從其他類122結構的超導體KxFe2Se2 (Tc ~ 32 K)，我們發現此類超導體與Ba1-xKxFe2As2 (I4/mmm)系統是類似的，而此類超導體將FeSe的超導溫度從8.5 K升高到32 K 的原因是因為將鹼土或是鹼金屬元素嵌入了FeSe的層狀結構中。因此我們試著用液態氨能夠溶解鹼土與鹼金屬融的特性(氨熱法)將Ba嵌入至中FeSe的層狀結構中。 而在四角結構β-Fe1+xSe 中，我們以x = 0.008 當做氨熱法的基材，因為在所有我們嘗試的比例中(0.005 到 0.02)，不論從XRD 還是在低溫時超導的相轉變溫度都有最好的表現。 而從中子繞射的實驗中得知Li0.5(NH3)Fe2Se2結構與122結構的超導相似只是原本鹼土族與鹼金屬的位置(2a)在結構中被NH3所佔據，另外Li也分別坐落在(2b)以及(4c)位置上，而經過反應後的樣本我們以XRD的相對強度模擬出類似的Ba0.5(NH3)Fe2Se2結構。此Ba0.5(NH3)Fe2Se2擁有39 K 的超導相轉變溫度，以及經由磁性測量結果推導出此樣本的μ0Hc1 ~ 21.1 G 與μ0Hc2 ~ 53.82 T。

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.