"111"型NaFeAs压力调控的结构及超导

 (Pressure-Induced Isostructural Phase Transition and Correlation of FeAs Coordination with the Superconducting Properties of 111-Type Na1-xFeAs

Q.Q. Liu, X.H. Yu, X.C. Wang, Z. Deng, Y.X. Lv, J.L. Zhu, S.J. Zhang, H.Z. Liu, W.G. Yang, L. Wang, H.K. Mao, G.Y. Shen, Z.Y. Lu, Y. Ren, Z.Q. Chen, Z.J. Lin, Y.S. Zha, C.Q. Jin

J. Am. Chem. Soc. 133, 7892 (2011)

  本工作研究了NaFeAs在压力条件下的结构演变以及其与超导转变温度的关联。实验发现NaFeAs在2GPa左右发生了等结构相变。超导铁砷层[FeAs]2中FeAs4四面体的As-Fe-As键角α(2-fold)在2GPa之前随压力增大而增大,并逐渐接近正四面体的夹角;当压力大于2GPa时,键角α随压力增大而减小。α随压力的变化趋势和NaFeAs的超导转变温度随压力的变化行为相同,这为寻求 NaFeAs压力调控的超导物性演化的结构起源提供了重要实验依据,也为从结构设计上探寻新的铁基超导提供了重要信息。同时本工作还发现了NaFeAs在20GPa左右发生了另外一个高压结构相变。
  中科院的科研进展物理所的科研动态中分别对该工作进行报道。  

 The effect of pressure on the crystalline structure and superconducting transition temperature (Tc) of the 111-type Na1-xFeAs system using in situ high-pressure synchrotron X-ray powder diffraction and diamond anvil cell techniques is studied. A pressure-induced tetragonal to tetragonal isostructural phase transition was found. The systematic evolution of the FeAs4 tetrahedron as a function of pressure based on Rietveld refinements on the powder X-ray diffraction patterns was obtained. The nonmonotonic Tc(P) behavior of Na1-xFeAs is found to correlate with the anomalies of the distance between the anion (As) and the iron layer as well as the bond angle of As-Fe-As for the two tetragonal phases. This behavior provides the key structural information in understanding the origin of the pressure dependence of Tc for 111-type iron pnictide superconductors. A pressure-induced structural phase transition is also observed at 20 GPa.

This work has been reported by Chinese Academy of Science and Institute of Physics respectively.