Superconductivities and structural properties of ternary Tiben Zrben Ta alloys

Superconductivities and structural properties of Ti-Zr-Ta ternary alloys are extensively investigated. The TiZrTa sample has a cubic structure (β -phase) and shows a sharp superconducting transition at a critical temperature (T_c) of about 7.3 K. In addition, two series of Ti-Zr-Ta alloys, with nominal compositions of Ti_65-xZr₃₅Ta_x and Ti_xZr_65-xTa₃₅ respectively, are prepared, and their superconductivities and crystal structures change regularly with the chemical composition. Our experimental study also indicates that the annealing processing of this kind of material can cause the transition temperature to increase and the highest T_c is observed to be about 8.3 K in annealed samples.     

铁基超导体的微结构和结构相变研究

铁基超导体表现出丰富的结构和物理性质,在多个典型体系中存在着结构相变和多重有序态之间的关联与竞争.例如,母相化合物LaFeAsO在150K附近发生从四方相（P4/nmm）到正交相（Cmma）的结构相变,同时其电输运性质和磁化率也表现出明显的反常行为.微结构分析发现,在CaFe2As2样品中,存在准周期调制结构,而且在低温区,122体系存在丰富的孪晶畴结构,这种孪晶结构是结构相变的直接结果.另外,在超导材料KxFe2-ySe2（0.7≤x≤0.8,0.2≤y≤0.4）中,Fe空位有序态和结构相分离是理解其结构,也是理解其磁性和输运性质的关键问题,特别是沿[130]晶体带轴方向的5倍超结构与系统的超导电性存在密切关系.     

Microstructure and structural phase transitions in iron-based superconductors

Crystal structures and microstructural features, such as structural phase transitions, defect structures, and chemical and structural inhomogeneities, are known to have profound effects on the physical properties of superconducting materials. Recently, many studies on the structural properties of Fe-based high-Tc superconductors have been published. This review article will mainly focus on the typical microstructural features in samples that have been well characterized by physical measurements. （i） Certain common structural features are discussed, in particular, the crystal structural features for different superconducting families, the local structural distortions in the Fe2Pn2 （Pn = P, As, Sb） or FeeCh2 （Ch = S, Se, Te） blocks, and the structural transformations in the 122 system. （ii） In FeTe（Se） （11 family）, the superconductivity, chemical and structural inhomogeneities are investigated and discussed in correlation with superconductivity. （iii） In the Ko.sFe1.6＋xSe2 system, we focus on the typical compounds with emphasis on the Fe-vacancy order and phase separations. The microstructural features in other superconducting materials are also briefly discussed.