"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。
　　中科院的科研进展和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.