High-temperature superconductivity is often found in the vicinity of antiferromagnetism. This is also true in LaFeAsOl-xFx （x ≤ 0.2,） and many other iron-based superconductors, which leads to proposals that superco...High-temperature superconductivity is often found in the vicinity of antiferromagnetism. This is also true in LaFeAsOl-xFx （x ≤ 0.2,） and many other iron-based superconductors, which leads to proposals that supercon- ductivity is mediated by fluctuations associated with the nearby magnetism. Here we report the discovery of a new superconductivity dome without low-energy magnetic fluctuations in LaFeAsO1-xFx with 0.25 ≤ x ≤ 0.75, where the maximal critical temperature Tc at Xopt =0.5-0.55 is even higher than that at x ≤0.2. By nuclear magnetic resonance and transmission electron microscopy, we show that a C4 rotation symmetry-breaking struc- tural transition takes place for x 〉 0.5 above To. Our results point to a new paradigm of high temperature superconductivity.展开更多
A new niobate compound Ba4LaTiNb3O15 has been synthesized and characterized. Through Rietveld refinement of X-ray powder diffraction data, Ba4LaTiNb3O15 is identified as the A5B4O15 type cation-deficient perovskites w...A new niobate compound Ba4LaTiNb3O15 has been synthesized and characterized. Through Rietveld refinement of X-ray powder diffraction data, Ba4LaTiNb3O15 is identified as the A5B4O15 type cation-deficient perovskites with space group of P3m1(164) and lattice constants a=0.572 38(1) nm, c=1.169 48(1) nm, V=0.331 81(1) nm3, and Z=1. The crystal structure can be described as consisting of identical perovskite-like blocks, four corner-sharing (Ba,La)O6 octahedra thick, separated by layers of vacant octahedral. The (Ba,La)-O bond lengths range from 0.267 to 0.321 nm and the (Ti,Nb)-O bond lengths range from 0.175 to 0.213 nm. The Ba4LaTiNb3O15 ceramic has a high dielectric constant of 53.3, high quality factors (Q) 3 650 (at 6.402 5 GHz), and low temperature variation of resonant frequency (τf) +69.3 × 10-6 K-1.展开更多
由5-溴-2-羟基苯基苯甲酮和苯甲酰肼通过缩合反应,合成了一种新的芳香酰腙化合物:5-溴-2-羟基苯基苯甲酮苯甲酰腙.通过X射线单晶衍射对该化合物进行晶体结构的表征.研究表明,该酰腙为单斜晶系,空间群为P2(1)/c,晶胞学数据为a=17.505(5)...由5-溴-2-羟基苯基苯甲酮和苯甲酰肼通过缩合反应,合成了一种新的芳香酰腙化合物:5-溴-2-羟基苯基苯甲酮苯甲酰腙.通过X射线单晶衍射对该化合物进行晶体结构的表征.研究表明,该酰腙为单斜晶系,空间群为P2(1)/c,晶胞学数据为a=17.505(5)nm,α=90.00°,b=13.761(4)nm,β=94.546(6)°,c=7.219(2)nm,γ=90.00°.V=1733.4(9)nm3,Z=4,μ=2.387mm-1,Dc=1.515mg/m3,F(000)=672,Final R indices[I>2sigma(I)]R1=0.0439,wR2=0.0813 R1=0.1051[I>2sigma(I)],wR2=0.1007(all data).展开更多
Ligularia sp. have the antibiotic and antiphlogistic effects. There have been many reports on the chemical constituents of them. However, no report has been given on the chemical constituents of Ligularia sagitta up t...Ligularia sp. have the antibiotic and antiphlogistic effects. There have been many reports on the chemical constituents of them. However, no report has been given on the chemical constituents of Ligularia sagitta up to now. In this note, we report a new compound which was isolated from the rhizome of the plant. It was identified as a lactone of new carbon skeleton by ELMS, <sup>13</sup>C NMR, DEPT, <sup>1</sup>H NMR and X-ray crystal structural analysis. It was named Sagittolactone.展开更多
基金Supported by the Strategic Priority Research Program of the Chinese Academy of Sciences under Grant No XDB07020200the National Basic Research Program of China under Grant Nos 2012CB821402,2011CBA00109 and 2011CBA00101the National Natural Science Foundation of China under Grant No 11204362
文摘High-temperature superconductivity is often found in the vicinity of antiferromagnetism. This is also true in LaFeAsOl-xFx （x ≤ 0.2,） and many other iron-based superconductors, which leads to proposals that supercon- ductivity is mediated by fluctuations associated with the nearby magnetism. Here we report the discovery of a new superconductivity dome without low-energy magnetic fluctuations in LaFeAsO1-xFx with 0.25 ≤ x ≤ 0.75, where the maximal critical temperature Tc at Xopt =0.5-0.55 is even higher than that at x ≤0.2. By nuclear magnetic resonance and transmission electron microscopy, we show that a C4 rotation symmetry-breaking struc- tural transition takes place for x 〉 0.5 above To. Our results point to a new paradigm of high temperature superconductivity.
文摘A new niobate compound Ba4LaTiNb3O15 has been synthesized and characterized. Through Rietveld refinement of X-ray powder diffraction data, Ba4LaTiNb3O15 is identified as the A5B4O15 type cation-deficient perovskites with space group of P3m1(164) and lattice constants a=0.572 38(1) nm, c=1.169 48(1) nm, V=0.331 81(1) nm3, and Z=1. The crystal structure can be described as consisting of identical perovskite-like blocks, four corner-sharing (Ba,La)O6 octahedra thick, separated by layers of vacant octahedral. The (Ba,La)-O bond lengths range from 0.267 to 0.321 nm and the (Ti,Nb)-O bond lengths range from 0.175 to 0.213 nm. The Ba4LaTiNb3O15 ceramic has a high dielectric constant of 53.3, high quality factors (Q) 3 650 (at 6.402 5 GHz), and low temperature variation of resonant frequency (τf) +69.3 × 10-6 K-1.
文摘由5-溴-2-羟基苯基苯甲酮和苯甲酰肼通过缩合反应,合成了一种新的芳香酰腙化合物:5-溴-2-羟基苯基苯甲酮苯甲酰腙.通过X射线单晶衍射对该化合物进行晶体结构的表征.研究表明,该酰腙为单斜晶系,空间群为P2(1)/c,晶胞学数据为a=17.505(5)nm,α=90.00°,b=13.761(4)nm,β=94.546(6)°,c=7.219(2)nm,γ=90.00°.V=1733.4(9)nm3,Z=4,μ=2.387mm-1,Dc=1.515mg/m3,F(000)=672,Final R indices[I>2sigma(I)]R1=0.0439,wR2=0.0813 R1=0.1051[I>2sigma(I)],wR2=0.1007(all data).
基金Project supported by the National Natural Science Foundation of China.
文摘Ligularia sp. have the antibiotic and antiphlogistic effects. There have been many reports on the chemical constituents of them. However, no report has been given on the chemical constituents of Ligularia sagitta up to now. In this note, we report a new compound which was isolated from the rhizome of the plant. It was identified as a lactone of new carbon skeleton by ELMS, <sup>13</sup>C NMR, DEPT, <sup>1</sup>H NMR and X-ray crystal structural analysis. It was named Sagittolactone.
