Systematical investigations of zero-field resistivity, magnetoresistance and magnetization were performed for a typical manganese compound La2/3Ca1/3MnO3. It is argued that the common origin for insulator-metal and pa...Systematical investigations of zero-field resistivity, magnetoresistance and magnetization were performed for a typical manganese compound La2/3Ca1/3MnO3. It is argued that the common origin for insulator-metal and paramagenetic ferromagnetic-transitions as well as colossal magnetoresistance is due to the formation of ferromagnetic clusters in the paramagnetic background. The transition to metallic state is resulted from percolation of ferromagnetic metallic clusters, while the colossal magnetoresistance is due to the application of magnetic field, which accelerates the growth of ferromagnetic metallic clusters and causes the shift of the onset temperature for the metallic percolation to higher temperature. Based on the random resistor network model, the zero-field resistivity versus temperature dependence is simulated by using experimental parameters, and experimental data well agree with those in whole temperature range, giving a strong support to our approach.展开更多
The magnetic and electrical transport properties of the colossal magnetoresistance material La_(2/3)Ca_(1/3)MnO_3 were studied. It is found that the insulator-metal transition is well consistent with the paramagnetic-...The magnetic and electrical transport properties of the colossal magnetoresistance material La_(2/3)Ca_(1/3)MnO_3 were studied. It is found that the insulator-metal transition is well consistent with the paramagnetic-ferromagnetic transition,and shifts to higher temperature with increasing applied magnetic field. These results suggest that the transport properties are triggered by the magnetic structure transition and consequently result in a CMR near T _C.展开更多
The development of negative permittivity materials in multifunctional applications requests expansion of their operating frequency and improvement of stability of negative permittivity.Low electron density is benefici...The development of negative permittivity materials in multifunctional applications requests expansion of their operating frequency and improvement of stability of negative permittivity.Low electron density is beneficial to reduce plasma frequency so that negative permittivity is achieved in kHz region.Negative permittivity achieved by percolating composites is restricted in practicality due to its instability nature at high temperatures.To achieve temperature-stable negative permittivity in kHz region,monophase La_(1-x)Ba_(x)CoO_(3)ceramics were prepared,and the transition from dielectric to metal was elaborated in the perspective of electrical conductivity and negative permittivity.The plasma-like negative permittivity is attained in kHz region,which is interpreted by the collective oscillation of low electron density.The temperature-stable negative permittivity is based on the fact that the plasmonic state will not be undermined at high temperatures.In addition,zero-crossing behavior of real permittivity is observed in La_(0.9)Ba_(0.1)CoO_(3)sample,which provides a promising alternative to designing epsilon-near-zero materials.This work makes the La_(1-x)Ba_(x)CoO_(3)system a source material for achieving effective negative permittivity.展开更多
The sol-gel process, sing aqueous solutions, is used for dip coating ontosubstrates of 316L stainless steel. A suitable coating of Li CoO_2 is achieved by varying thethickness and heat treating at 650 deg C for 3 h. T...The sol-gel process, sing aqueous solutions, is used for dip coating ontosubstrates of 316L stainless steel. A suitable coating of Li CoO_2 is achieved by varying thethickness and heat treating at 650 deg C for 3 h. Thermal analysis, X-ray diffraction analysis andSEM are carried out to characterize the microstructure of the coatings. The results show that thecoating transforms from an amorphous gel to crystalline phases above 350 deg C, and show a porousstructure. The phase transition mechanism is discussed.展开更多
Controlling oxygen redox reactions in transition metal oxides offers an attractive route to tune their physical properties;a topotactic structural transformation from their parent phases effectively modifies the elect...Controlling oxygen redox reactions in transition metal oxides offers an attractive route to tune their physical properties;a topotactic structural transformation from their parent phases effectively modifies the electronic state. In this work, infinitelayered SrFeO_(2) thin films were produced from brownmillerite SrFeO_(2.5) via low-temperature hydro-reduction. After the structural transition, their out-of-plane lattice constants dramatically shrank by 12%;tensilely strained samples exhibited metallic character, whereas the compressively strained ones maintained the insulating behavior of their bulk form. According to X-ray linear dichroism results, this strain-mediated electronic anisotropy may be attributed to electron redistribution within degenerated orbitals. This suggests a possible mechanism for the metallic conductivity of infinite-layered SrFeO_(2), giving a hint for understanding emergent quantum phenomena, such as the recently discovered superconductivity in nickelates, and stimulating various applications, including in ionic conductivity and oxygen catalysis.展开更多
The heat and mass transfer characteristics under frosting on surface of heat exchanger were experimentally investigated in different conditions of air temperature, relative humidity, and face velocity. The heat transf...The heat and mass transfer characteristics under frosting on surface of heat exchanger were experimentally investigated in different conditions of air temperature, relative humidity, and face velocity. The heat transfer and heat transfer coefficient decreased faster with the high relative humidity, low air temperature and initial face velocity. The air pressure drop rose faster with the high relative humidity and low air velocity.展开更多
基金Funded by the National "973" Project of China (No.2006CB921606)the Foundation from the Ministry of the National Education (Nos. 309020and 20060487011)
文摘Systematical investigations of zero-field resistivity, magnetoresistance and magnetization were performed for a typical manganese compound La2/3Ca1/3MnO3. It is argued that the common origin for insulator-metal and paramagenetic ferromagnetic-transitions as well as colossal magnetoresistance is due to the formation of ferromagnetic clusters in the paramagnetic background. The transition to metallic state is resulted from percolation of ferromagnetic metallic clusters, while the colossal magnetoresistance is due to the application of magnetic field, which accelerates the growth of ferromagnetic metallic clusters and causes the shift of the onset temperature for the metallic percolation to higher temperature. Based on the random resistor network model, the zero-field resistivity versus temperature dependence is simulated by using experimental parameters, and experimental data well agree with those in whole temperature range, giving a strong support to our approach.
文摘The magnetic and electrical transport properties of the colossal magnetoresistance material La_(2/3)Ca_(1/3)MnO_3 were studied. It is found that the insulator-metal transition is well consistent with the paramagnetic-ferromagnetic transition,and shifts to higher temperature with increasing applied magnetic field. These results suggest that the transport properties are triggered by the magnetic structure transition and consequently result in a CMR near T _C.
基金supported by the National Natural Science Foundation of China(Nos.51771104,51871146,51971119)the Natural Science Foundation of Shandong Province(No.ZR2020YQ32)the Innovation Program of Shanghai Municipal Education Commission(No.2019-01-07-00-10-E00053)。
文摘The development of negative permittivity materials in multifunctional applications requests expansion of their operating frequency and improvement of stability of negative permittivity.Low electron density is beneficial to reduce plasma frequency so that negative permittivity is achieved in kHz region.Negative permittivity achieved by percolating composites is restricted in practicality due to its instability nature at high temperatures.To achieve temperature-stable negative permittivity in kHz region,monophase La_(1-x)Ba_(x)CoO_(3)ceramics were prepared,and the transition from dielectric to metal was elaborated in the perspective of electrical conductivity and negative permittivity.The plasma-like negative permittivity is attained in kHz region,which is interpreted by the collective oscillation of low electron density.The temperature-stable negative permittivity is based on the fact that the plasmonic state will not be undermined at high temperatures.In addition,zero-crossing behavior of real permittivity is observed in La_(0.9)Ba_(0.1)CoO_(3)sample,which provides a promising alternative to designing epsilon-near-zero materials.This work makes the La_(1-x)Ba_(x)CoO_(3)system a source material for achieving effective negative permittivity.
基金This project is supported by Energy Research Corp., USA.
文摘The sol-gel process, sing aqueous solutions, is used for dip coating ontosubstrates of 316L stainless steel. A suitable coating of Li CoO_2 is achieved by varying thethickness and heat treating at 650 deg C for 3 h. Thermal analysis, X-ray diffraction analysis andSEM are carried out to characterize the microstructure of the coatings. The results show that thecoating transforms from an amorphous gel to crystalline phases above 350 deg C, and show a porousstructure. The phase transition mechanism is discussed.
基金supported by the National Key Basic Research Program of China(Grant Nos.2020YFA0309100,and 2019YFA0308500)the Program for the Innovation Team of Science and Technology in University of Henan(Grant No.20IRTSTHN014)+4 种基金the Excellent Youth Foundation of He’nan Scientific Committee(Grant No.202300410356)the National Natural Science Foundation of China(Grant No.11974390)the Beijing Nova Program of Science and Technology(Grant No.Z191100001119112)the Beijing Natural Science Foundation(Grant No.2202060)the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB33030200)。
文摘Controlling oxygen redox reactions in transition metal oxides offers an attractive route to tune their physical properties;a topotactic structural transformation from their parent phases effectively modifies the electronic state. In this work, infinitelayered SrFeO_(2) thin films were produced from brownmillerite SrFeO_(2.5) via low-temperature hydro-reduction. After the structural transition, their out-of-plane lattice constants dramatically shrank by 12%;tensilely strained samples exhibited metallic character, whereas the compressively strained ones maintained the insulating behavior of their bulk form. According to X-ray linear dichroism results, this strain-mediated electronic anisotropy may be attributed to electron redistribution within degenerated orbitals. This suggests a possible mechanism for the metallic conductivity of infinite-layered SrFeO_(2), giving a hint for understanding emergent quantum phenomena, such as the recently discovered superconductivity in nickelates, and stimulating various applications, including in ionic conductivity and oxygen catalysis.
文摘The heat and mass transfer characteristics under frosting on surface of heat exchanger were experimentally investigated in different conditions of air temperature, relative humidity, and face velocity. The heat transfer and heat transfer coefficient decreased faster with the high relative humidity, low air temperature and initial face velocity. The air pressure drop rose faster with the high relative humidity and low air velocity.
