铁基122体系超导体的微结构与物性研究  

Structural phase transitions, phase separation and physical properties for the 122-system iron-based superconductors

作　　者：孙开[1] 徐程超 张瑞心 田焕芳[1] 李子安[1] 杨槐馨[1] 李建奇[1] 

机构地区：[1]中国科学院物理研究所,北京100190

出　　处：《科学通报》2017年第34期3981-3994,共14页Chinese Science Bulletin

基　　金：国家自然科学基金(11604372;11274368;51272277;91221102;11190022;11474323;91422303)资助

摘　　要：铁基超导体的发现再次掀起了高温超导的研究热潮,由于铁基高温超导体具有丰富的结构和物理性质,近十年来一直是科学界的重要研究领域之一.目前在多个典型的铁基超导体系中已经证实,存在着结构相变和多重有序态之间的关联与竞争.微结构研究和原位电子显微镜分析表明,典型122超导体系AFe_2As_2(A=Ca,Sr,Ba,Eu等)在低温区发生四方相到正交相结构相变,产生丰富的孪晶和微结构现象.在CaFe_2As_2中存在织呢(tweed)结构,并在Ca原子层引起准周期结构调制,平均周期为40 nm.在K_yFe_(2-x)Se_2超导体系中,存在丰富的相分离现象,在a-b面内出现了复杂的畴结构.此外,A位元素的替代对AFe_2As_2体系母相材料的结构特性和低温结构相变有重要影响,从而引起超导电性改变.The discovery of iron-based superconductors stimulated the second research upsurge for high-temperature superconductors, which have been considered as one of the significant research field from both academic and technological points of view. It is noted that the studies of iron-based superconductors have brought a great development of a large number of experimental technologies and theoretical researches in superconductivity physics. The remarkable correlations between structural transitions and multiple ordered states have been observed in the typical iron-based superconductors. According to the microstructure analyses and in-situ transmission electron microscopy（TEM） investigations, AFe2As2（A=Ba, Sr and Ca） iron-based superconducting materials often show up a structural transition from tetragonal phase to orthorhombic phase from room temperature down to 20 K, resulting in visible twinning domains in the orthorhombic phase. The tetragonal SrFe2As2 samples, consistent with X-ray and neutron-diffraction data, undergo the tetragonalorthorhombic phase transition at about 205 K and show clear twin domains in the orthorhombic phase. On the other hand, TEM observations of CaFe2As2 reveal the presence of a pseudoperiodic structural modulation with a periodicity of around 40 nm at room temperature. This quasi-periodicity structural modulation is likely related to the local structural distortions within the Ca layers. In situ cooling TEM observations of CaFe2As2 reveal the presence of complex domain structures in the low-temperature orthorhombic phase. Phase separation and structural inhomogeneity as critical structural issues have been extensively investigated in a variety of strongly correlated systems. The phase separations associated with structural domains result visibly structural alterations in KyFe（2-x）Se2 system. Structural investigations by means of TEM on K（0.8）FexSe2 and KFexSe2, with 1.5≤x≤1.8, have revealed a rich variety of microstructure phenomena. Materials with 1.5≤x≤1.6 often sho

关 键 词：铁基超导 结构类型 122体系 结构相变 相分离 物性 

分 类 号：O511.3[一般工业技术—材料科学与工程]