The ab initio method has been used to study the 1-3 H transfer reaction on formamidine substituted by halogen. The calculation results show that the substituted halogen has two effects on the 1-3 H transfer reaction...The ab initio method has been used to study the 1-3 H transfer reaction on formamidine substituted by halogen. The calculation results show that the substituted halogen has two effects on the 1-3 H transfer reaction: decreasing the activation energy and stabilizing the C=N double bond owing to the conjugative effect of p-π-p of products and transition states.展开更多
BaFeO_(3-δ)-derived perovskites are promising cathodes for intermediate temperature solid oxide fuel cells.The activity of these perovskites depends on the number of oxygen vacancies in their lattice,which can be tun...BaFeO_(3-δ)-derived perovskites are promising cathodes for intermediate temperature solid oxide fuel cells.The activity of these perovskites depends on the number of oxygen vacancies in their lattice,which can be tuned by cationic substitution.Our first-principle calculations show that Ag is a promising substitute for the Fe site,resulting in a reduced oxygen vacancy formation energy compared with the pristine BaFeO_(3-δ).Ag has limited solubility in perovskites,and its introduction generates an Ag metal secondary phase,which influences the cathode performances.In this work,we investigate the matter,using a Ba0:9La0:1Fe_(1-x)AgxO_(3-δ)series of materials as a case study.Acknowledging the limited solubility of Ag in Ba0:9La0:1Fe_(1-x)AgxO_(3-δ),we aim to distinguish the effects of Ag substitution from those of the Ag secondary phase.We observed that Ag substitution increases the number of oxygen vacancies,confirming our calculations,and facilitates the oxygen incorporation.However,Ag substitution lowers the number of holes,in this way reducing the electronic p-type conductivity.On the other hand,Ag metal positively affects the electronic conductivity and helps the redistribution of the electronic charge at the cathode-electrolyte interface.展开更多
Investigation of the substitution process can provide a better understanding of the superconducting mechanisms in cuprous oxide materials. In this work the effects of substitution Lanthanum (La) for Gadolinium (Gd) on...Investigation of the substitution process can provide a better understanding of the superconducting mechanisms in cuprous oxide materials. In this work the effects of substitution Lanthanum (La) for Gadolinium (Gd) on the structure and oxygen content for x = 0.0 - 0.5 in the compound Gd1-xLaxBa2Cu3O7-δ (GLBCO-123 phase) have been investigated. Samples were synthesized by using a wet-mixing method from powders of Gd2O2, La2O2, BaO, CuO, and solution of HNO3. Based on the analysis of XRD data and SEM-EDXA, it confirms that the sample has formed the GLBCO-123 phase, as expected. It has been obtained that the lattice parameters a and c are increased while the parameter b is slightly decreased with increasing content of Lanthanum. The oxygen content slightly decreased and structure of the Gd1-xLaxBa2Cu3O7-δ phase changed from orthorhombic to tetragonal with increasing the content of Lanthanum.展开更多
In an effort to improve the performance of superconductors in the field and high temperatures it is important to study the superconducting mechanism. For this reason, the cation substitution can be conducted. One of t...In an effort to improve the performance of superconductors in the field and high temperatures it is important to study the superconducting mechanism. For this reason, the cation substitution can be conducted. One of the high Tc superconductors Gd1Ba2Cu3O7−δ phase with Sr substitution has been synthesized, i.e. Gd1(Ba2−xSrx)Cu3O7−δ compound. The sample was synthesized by using a solid-state reaction method with a wet mixing, sintered for 12 hours at temperature 900°C. The synthesis results are characterized by using XRD. The results of Match-3 software analysis showed high (higher 85%) Gd1Ba2Cu3O7−δ phase was formed. The Sr substitution causes changes to the structure, i.e. the lattice parameters a, b and c, where the orthorhombicity tends to decrease with increasing Sr content. Refinement results show that based on the oxygen occupancy, the total oxygen content tends to increase.展开更多
VO4^3- anion was used to partially substitute for PO43 in the Nasicon compound of LiSn2（PO4）3 via a sol-gel method. XRD analysis revealed that the VO4^3-substituted samples did not have a single LiSn2（PO4）3 phase,...VO4^3- anion was used to partially substitute for PO43 in the Nasicon compound of LiSn2（PO4）3 via a sol-gel method. XRD analysis revealed that the VO4^3-substituted samples did not have a single LiSn2（PO4）3 phase, and some secondary phases like SnO2 and SnP2O7 appeared. Introduction of the VO4^3- anion did not prevent the LiSn2（PO4）3 compound from decomposing during the initial lithiation; however the VO4^3- anion substitution remarkably enhanced the rate capability and cycling performance of the products because they reduced the charge transfer hnpedance, increased the lithium ion diffusion, and strengthened the role of the Li3PQ matrix due to the precipitation of the Li3V04 phase, Of the substituted samples, the sample with a nominal composition of LiSn2（PO4）2.5（VO4）0.5 delivered a capacity of 449.2 mA-h/g at a rate of 0.25 C after 25 cycles and 373.8 mA.h/g at 2 C rate. Those values surpassed some previous reports on LiSn2（PO4）3 and the LiSnz（PO4）3/C composites. Accordingly, the partial substitution of phosphorus by vanadium in LiSn2（PO4）3 is a feasible technique to remarkably improve its electrochemical properties.展开更多
An efficient regioselective Friedel-Crafts hydroxyalkylation of N-substituted glyoxylamide with various indoles catalyzed by Lewis acids was developed. The reactions proceeded smoothly at room temperature and the 2-hy...An efficient regioselective Friedel-Crafts hydroxyalkylation of N-substituted glyoxylamide with various indoles catalyzed by Lewis acids was developed. The reactions proceeded smoothly at room temperature and the 2-hydroxy-2-（1H-indol-3-yl）-N-substituted acetamide resulted from the reactions catalyzed by FeSO4 were synthesized in excellent yields （up to 93%）. While the bisindole compounds were obtained when FeCl3 was used as a catalyst in excellent yields （up to 92%）. A possible mechanism was proposed.展开更多
This paper reports the experimental results of the investigation on elemental substitution effects in YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-δ</sub> and the new physical ideas deduce...This paper reports the experimental results of the investigation on elemental substitution effects in YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-δ</sub> and the new physical ideas deduced comprehensively. It is shown that all the orthorhombic crystalline structure, oxygen content, oxidation valence of Cu atoms, and metal-semiconductor （insulator） transition are only the extrinsic factors deter mining the T<sub>c</sub> of the systems, and there are two mechanisms of substitution effects, namely the mechanism of the substitution effects outside the CuO<sub>2</sub> planes and that within the CuO<sub>2</sub> planes. We suggest that the mobile carrier concentration and the dynamic, short-range antiferromagnetic correlation between Cu（2） atoms on the CuO<sub>2</sub> planes are the two intrinsic factors determining the high T<sub>c</sub> superconductivity.展开更多
1 Introduction The infrared and Raman spectroscopy are the active tools for studying the lattice vibrations. Since the discovery of high-temperature superconductor, they have been efficiently used to study the novel o...1 Introduction The infrared and Raman spectroscopy are the active tools for studying the lattice vibrations. Since the discovery of high-temperature superconductor, they have been efficiently used to study the novel oxide superconductor. Some key results were obtained to provide proofs for determining the mechanism of superconductivity. The Pr<sub>x</sub>Y<sub>1-x</sub>Ba<sub>2</sub>Cu<sub>3</sub>O<sub>7-δ</sub>, is a useful system for studying the high-temperature superconducting mechanism since all展开更多
Tandem asymmetric double Michael addition/internal nucleophilic substitution of the novel chiral source, 5-(l-menthyloxy)-3-bromo-2(5H)-furanone with nucleophilic alcohol compounds has been investigated. The tandem as...Tandem asymmetric double Michael addition/internal nucleophilic substitution of the novel chiral source, 5-(l-menthyloxy)-3-bromo-2(5H)-furanone with nucleophilic alcohol compounds has been investigated. The tandem asymmetric reaction can afford four new stereogenic centers with one reaction and give optically pure spiro-cyclopropane derivatives 5a--5d which are difficult to obtain by routine methods. The synthetic method for 5a--5d was studied in detail and the new compounds were identified on the basis of their analytical data and spectroscopic data, such as [α]^(20),IR,~1H NMR,^(13)C NMR, MS and elementary analysis. The absolute configuration of the sprio [5-l-menthyloxy-3-bromo butyrolactocyclopropane-3″, 3′(4′-methyloxy-5′-menthyloxybutyrolactone)] (5a) was established by X-ray crystallography. The work can provide important synthetic strategy in synthesis of some new optically active spiro-cyclopropane analogues and some biologically active molecules with complex structure.展开更多
基金Supported by the Yunnan Provincial Science and Technology Department (2003A0003M)
文摘The ab initio method has been used to study the 1-3 H transfer reaction on formamidine substituted by halogen. The calculation results show that the substituted halogen has two effects on the 1-3 H transfer reaction: decreasing the activation energy and stabilizing the C=N double bond owing to the conjugative effect of p-π-p of products and transition states.
基金The authors gratefully acknowledge the Research Grant Council of Hong Kong for support through the projects 16201820,and 16206019.
文摘BaFeO_(3-δ)-derived perovskites are promising cathodes for intermediate temperature solid oxide fuel cells.The activity of these perovskites depends on the number of oxygen vacancies in their lattice,which can be tuned by cationic substitution.Our first-principle calculations show that Ag is a promising substitute for the Fe site,resulting in a reduced oxygen vacancy formation energy compared with the pristine BaFeO_(3-δ).Ag has limited solubility in perovskites,and its introduction generates an Ag metal secondary phase,which influences the cathode performances.In this work,we investigate the matter,using a Ba0:9La0:1Fe_(1-x)AgxO_(3-δ)series of materials as a case study.Acknowledging the limited solubility of Ag in Ba0:9La0:1Fe_(1-x)AgxO_(3-δ),we aim to distinguish the effects of Ag substitution from those of the Ag secondary phase.We observed that Ag substitution increases the number of oxygen vacancies,confirming our calculations,and facilitates the oxygen incorporation.However,Ag substitution lowers the number of holes,in this way reducing the electronic p-type conductivity.On the other hand,Ag metal positively affects the electronic conductivity and helps the redistribution of the electronic charge at the cathode-electrolyte interface.
文摘Investigation of the substitution process can provide a better understanding of the superconducting mechanisms in cuprous oxide materials. In this work the effects of substitution Lanthanum (La) for Gadolinium (Gd) on the structure and oxygen content for x = 0.0 - 0.5 in the compound Gd1-xLaxBa2Cu3O7-δ (GLBCO-123 phase) have been investigated. Samples were synthesized by using a wet-mixing method from powders of Gd2O2, La2O2, BaO, CuO, and solution of HNO3. Based on the analysis of XRD data and SEM-EDXA, it confirms that the sample has formed the GLBCO-123 phase, as expected. It has been obtained that the lattice parameters a and c are increased while the parameter b is slightly decreased with increasing content of Lanthanum. The oxygen content slightly decreased and structure of the Gd1-xLaxBa2Cu3O7-δ phase changed from orthorhombic to tetragonal with increasing the content of Lanthanum.
基金This report is part of the fundamental research report with contract No.486 127/UN14.2/PNL.01.03.00/2016.
文摘In an effort to improve the performance of superconductors in the field and high temperatures it is important to study the superconducting mechanism. For this reason, the cation substitution can be conducted. One of the high Tc superconductors Gd1Ba2Cu3O7−δ phase with Sr substitution has been synthesized, i.e. Gd1(Ba2−xSrx)Cu3O7−δ compound. The sample was synthesized by using a solid-state reaction method with a wet mixing, sintered for 12 hours at temperature 900°C. The synthesis results are characterized by using XRD. The results of Match-3 software analysis showed high (higher 85%) Gd1Ba2Cu3O7−δ phase was formed. The Sr substitution causes changes to the structure, i.e. the lattice parameters a, b and c, where the orthorhombicity tends to decrease with increasing Sr content. Refinement results show that based on the oxygen occupancy, the total oxygen content tends to increase.
基金Supported by the Natural Science Foundation of Hebei Province, China（No.E2016202358）.
文摘VO4^3- anion was used to partially substitute for PO43 in the Nasicon compound of LiSn2（PO4）3 via a sol-gel method. XRD analysis revealed that the VO4^3-substituted samples did not have a single LiSn2（PO4）3 phase, and some secondary phases like SnO2 and SnP2O7 appeared. Introduction of the VO4^3- anion did not prevent the LiSn2（PO4）3 compound from decomposing during the initial lithiation; however the VO4^3- anion substitution remarkably enhanced the rate capability and cycling performance of the products because they reduced the charge transfer hnpedance, increased the lithium ion diffusion, and strengthened the role of the Li3PQ matrix due to the precipitation of the Li3V04 phase, Of the substituted samples, the sample with a nominal composition of LiSn2（PO4）2.5（VO4）0.5 delivered a capacity of 449.2 mA-h/g at a rate of 0.25 C after 25 cycles and 373.8 mA.h/g at 2 C rate. Those values surpassed some previous reports on LiSn2（PO4）3 and the LiSnz（PO4）3/C composites. Accordingly, the partial substitution of phosphorus by vanadium in LiSn2（PO4）3 is a feasible technique to remarkably improve its electrochemical properties.
基金the National Natural Science Foundation of China (Nos. 21472130, 81373259) for financial support of this study
文摘An efficient regioselective Friedel-Crafts hydroxyalkylation of N-substituted glyoxylamide with various indoles catalyzed by Lewis acids was developed. The reactions proceeded smoothly at room temperature and the 2-hydroxy-2-（1H-indol-3-yl）-N-substituted acetamide resulted from the reactions catalyzed by FeSO4 were synthesized in excellent yields （up to 93%）. While the bisindole compounds were obtained when FeCl3 was used as a catalyst in excellent yields （up to 92%）. A possible mechanism was proposed.
基金Project supported by the Combined Centre of Research and Development of Superconduction Technology and the National Natural Science Foundation of China.
文摘This paper reports the experimental results of the investigation on elemental substitution effects in YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-δ</sub> and the new physical ideas deduced comprehensively. It is shown that all the orthorhombic crystalline structure, oxygen content, oxidation valence of Cu atoms, and metal-semiconductor （insulator） transition are only the extrinsic factors deter mining the T<sub>c</sub> of the systems, and there are two mechanisms of substitution effects, namely the mechanism of the substitution effects outside the CuO<sub>2</sub> planes and that within the CuO<sub>2</sub> planes. We suggest that the mobile carrier concentration and the dynamic, short-range antiferromagnetic correlation between Cu（2） atoms on the CuO<sub>2</sub> planes are the two intrinsic factors determining the high T<sub>c</sub> superconductivity.
文摘1 Introduction The infrared and Raman spectroscopy are the active tools for studying the lattice vibrations. Since the discovery of high-temperature superconductor, they have been efficiently used to study the novel oxide superconductor. Some key results were obtained to provide proofs for determining the mechanism of superconductivity. The Pr<sub>x</sub>Y<sub>1-x</sub>Ba<sub>2</sub>Cu<sub>3</sub>O<sub>7-δ</sub>, is a useful system for studying the high-temperature superconducting mechanism since all
基金Project supported by the National Natural Science Foundation of China (Grant No. 29672004)
文摘Tandem asymmetric double Michael addition/internal nucleophilic substitution of the novel chiral source, 5-(l-menthyloxy)-3-bromo-2(5H)-furanone with nucleophilic alcohol compounds has been investigated. The tandem asymmetric reaction can afford four new stereogenic centers with one reaction and give optically pure spiro-cyclopropane derivatives 5a--5d which are difficult to obtain by routine methods. The synthetic method for 5a--5d was studied in detail and the new compounds were identified on the basis of their analytical data and spectroscopic data, such as [α]^(20),IR,~1H NMR,^(13)C NMR, MS and elementary analysis. The absolute configuration of the sprio [5-l-menthyloxy-3-bromo butyrolactocyclopropane-3″, 3′(4′-methyloxy-5′-menthyloxybutyrolactone)] (5a) was established by X-ray crystallography. The work can provide important synthetic strategy in synthesis of some new optically active spiro-cyclopropane analogues and some biologically active molecules with complex structure.
