X射线粉晶衍射在新功能材料探索中的一些应用

1912年发现的晶体X射线衍射现象标志着现代晶体学的诞生,对近代物理学乃至整个科学领域的发展都产生了极为深刻的影响。X射线粉晶衍射将结构分析拓展到多晶材料,成为物理学、化学和材料科学重要的研究手段。文章结合作者在硼酸盐及铁基超导体研究领域的典型工作,介绍了X射线粉晶衍射在新型功能材料探索中的一些应用。随着新方法和新技术的不断出现和完善,相信未来X射线粉晶衍射在新材料探索和其他应用领域将起到越来越重要的作用。     

新型FeSe基超导材料研究进展

FeSe基超导体作为铁基超导材料家族的重要组成部分,已经成为凝聚态物理研究的一个热点领域,对这类超导材料的探索和制备是研究其物理性质的基础.目前,对于FeSe基超导材料的探索主要集中于插层和外延单层FeSe薄膜.其中,通过插层方法获得的FeSe基超导材料具有独特的性质,且种类众多.本文介绍了近年来发现的一系列FeSe基高温超导材料,涵盖K_xFe₂Se₂,A_xNH₃FeSe,LiOHFeSe和有机分子插层FeSe等,并针对各种材料,简述了其性质及影响.     

Bandgap narrowing in the layered oxysulfide semiconductor Ba_3Fe_2O_5Cu_2S_2: Role of FeO_2 layer

A new layered Cu-based oxychalcogenide Ba_3Fe_2O_5Cu_2S_2 has been synthesized and its magnetic and electronic properties were revealed. Ba_3Fe_2O_5Cu_2S_2 is built up by alternatively stacking [Cu_2S_2]~(2-) layers and iron perovskite oxide[(FeO_2)(BaO)(FeO_2)]~(2-)layers along the c axis that are separated by barium ions with Fe~(3+) fivefold coordinated by a square-pyramidal arrangement of oxygen. From the bond valence arguments, we inferred that in layered CuC h-based(Ch =S, Se, Te) compounds the +3 cation in perovskite oxide sheet prefers a square pyramidal site, while the lower valence cation prefers the square planar sites. The studies on susceptibility, transport, and optical reflectivity indicate that Ba_3Fe_2O_5Cu_2S_2 is an antiferromagnetic semiconductor with a Ne′el temperature of 121 K and an optical bandgap of 1.03 eV. The measurement of heat capacity from 10 K to room temperature shows no anomaly at 121 K. The Debye temperature is determined to be 113 K. Theoretical calculations indicate that the conduction band minimum is predominantly contributed by O 2p and 3 d states of Fe ions that antiferromagnetically arranged in FeO_2 layers. The Fe 3d states are located at lower energy and result in a narrow bandgap in comparison with that of the isostructural Sr_3Sc_2O_5Cu_2S_2.     

Exploring FeSe-based superconductors by liquid ammonia method

Our recent progress on the preparation of a series of new FeSe-based superconductors and the clarification of SC phases in potassium-intercalated iron selenides are reviewed here. By the liquid ammonia method, metals Li, Na, Ca, Sr, Ba, Eu, and Yb are intercalated in between FeSe layers and form superconductors with transition temperatures of 30 K～46 K, which cannot be obtained by high-temperature routes. In the potassium-intercalated iron selenides, we demonstrate that at least two SC phases exist, K x Fe 2 Se 2 (NH 3 ) y (x ≈ 0.3 and 0.6), determined mainly by the concentration of potassium. NH 3 has little, if any, effect on superconductivity, but plays an important role in stabilizing the structures. All these results provide a new starting point for studying the intrinsic properties of this family of superconductors, especially for their particular electronic structures.     

Nanocrystallization behaviour of a ternary amorphous alloy during isothermal annealing： a Monte Carlo simulation

The nanocrystallization behaviour of Zr70Cu20Ni10 metallic glass during isothermal annealing is studied by employing a Monte Carlo simulation incorporating with a modified Ising model and a Q-state Potts model. Based on the simulated microstructure and differential scanning calorimetry curves, we find that the low crystal-amorphous interface energy of Ni plays an important role in the nanocrystallization of primary Zr2Ni. It is found that when T〈T1max （where T1max is the temperature with maximum nucleation rate）, the increase of temperature results in a larger growth rate and a much finer mierostrueture for the primary Zr2Ni, which accords with the microstructure evolution in ＂flash annealing＂. Finally, the Zr2Ni/Zr2Cu interface energy σG contributes to the pinning effect of the primary nano-sized Zr2Ni grains in the later formed normal Zr2Cu grains.     

新型铁基超导体材料的研究进展

文章主要介绍了碱金属插层法合成新型铁基超导体的研究进展.通过采用碱金属K对FeSe层状材料插层的方法,得到了一种新型的铁基超导体K0.8Fe1.7Se2,并对该材料的晶体结构与物性进行了研究.结果表明,该化合物的超导转变温度达到30K,这是FeSe体系在常压下的最高超导转变温度.同时,观察到该体系中存在转变温度为43K的超导相,但未得到纯相.通过磁性元素Co的掺杂研究,进一步加深了对K0.8Fe1.7Se2体系超导演化规律的认识.该超导体的发现对深入认识铁基超导体的超导机理,探索具有更高超导转变温度的铁基超导体具有重要意义.