Superparamagnetic monodisperse Mg0.8Mn0.2Fe2O4 nanoparticles have been successfully synthesized in liquid polyol at elevated temperature of 200 °C. Diethylene glycol（DEG） used here plays dual role in synthesis ...Superparamagnetic monodisperse Mg0.8Mn0.2Fe2O4 nanoparticles have been successfully synthesized in liquid polyol at elevated temperature of 200 °C. Diethylene glycol（DEG） used here plays dual role in synthesis as it acts as reducing agent and alternatively coats the surface of nanoparticles while synthesis and thereby maintaining uniform size and dispersibility. Powder X-ray diffraction（XRD） and magnetic measurements showed that the sample is cubic spinel and superparamagnetic at room temperature. Raman spectra confirmed the formation of the Mg0.8Mn0.2Fe2O4 nanoparticles.The nanoparticles exhibit very good stability in water due to in situ coating with DEG molecules.展开更多
Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ phosphors were synthesized by solid-state reaction technique. The crystalline phase and luminescence performances of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ were observe...Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ phosphors were synthesized by solid-state reaction technique. The crystalline phase and luminescence performances of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ were observed by X-ray powder diffractometer（XRD）, transmission electron microscope（TEM）, photoluminescence spectrometer and brightness meter, respectively. The addition of Ag~＋ can diminish in the crystal particle sizes of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）. Because Ag＋ can reduce the concentration of the undesirable defects in the phosphor, luminescence intensity of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ is 2.3 times as high as that of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）at the same preparation condition. The effect of Ag＋ on the persistent afterglow properties is to deepen the energy storage traps and enhance the energy transfer efficiency from Ca_（0.9）Mg_（0.1）TiO_3 to Pr^（3＋）. The persistent afterglow properties of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ are better than those of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋） at the same preparation condition. In conclusion,Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ phosphor with molar ratio of Ag~＋to Pr^（3＋） 3：1 obtained at 900 ℃ for 4 h exhibits the optimal photoluminescence performances.展开更多
Amorphous structure generated by high-energy ball miller(BM)is often used as a precursor for generating nanocomposites through controlled devitrification.The amorphous forming composition range of ternary Al-Cu-Zr sys...Amorphous structure generated by high-energy ball miller(BM)is often used as a precursor for generating nanocomposites through controlled devitrification.The amorphous forming composition range of ternary Al-Cu-Zr system was calculated using the extended Miedema’s semiempirical model.Eleven compositions of Al-Cu-Zr system showed a wide range of negative enthalpy of mixing(-ΔH^(mix))and amorphization(-ΔH^(amor))among the constituent elements was selected for synthesis by BM.They yielded either nanocomposites of partial amorphous and crystalline structure or no amorphous phase at all in the as-milled condition.The Al_(88)Cu_(6)Zr_(6) alloy with relatively small negativeΔH^(mix)(-0.4 kJ/mol)andΔH^(amor)(-14.8 kJ/mol)became completely amorphous after 120 h of milling.展开更多
The growth mechanisms of high temperature Yttrium- and Bismuth-based-superconductors were investigated at nanoscale. We started with studying the growth relationships among the three phases of Bi-2201, Bi-2212, and Bi...The growth mechanisms of high temperature Yttrium- and Bismuth-based-superconductors were investigated at nanoscale. We started with studying the growth relationships among the three phases of Bi-2201, Bi-2212, and Bi-2233, and then extended to another growth mechanism of Bi-2223 and the growth of yttrium-based high-temperature nanosuperconductors （nano-YBCO）. A time dependence of growth experiment was performed. In this experiment, the Bi-based superconductors grew within different sintering periods, and its three phases were determined by X-ray diffraction. And then, a time dependence of growth model was suggested to explain the experimental facts. With this model, governing equations were derived to quantitatively describe the growth and decomposition mechanisms during sintering period. The results calculated from the derived equations were well in agreement with the experimental data. We also suggested an alternative growth mechanism for the Bi-2223 phase, which was supported by an observation of transmission electron microscopy （TEM）. The nano-YBCO also grew, and their orthorhombic crystal structures were determined by the TEM. The superconducting properties of Bi-2223 were investigated by the measurements of ac magnetic susceptibility. It is expected that the derived equations will fit the alternative experimental growth mechanism of the Bi-2223 phase and the nano-YBCO growth mechanism, too.展开更多
基金the Council of Scientific and Industrial Research, India for the award of senior research fellowship (File. 09/1077/(0001)/ 2012/EMR-1)
文摘Superparamagnetic monodisperse Mg0.8Mn0.2Fe2O4 nanoparticles have been successfully synthesized in liquid polyol at elevated temperature of 200 °C. Diethylene glycol（DEG） used here plays dual role in synthesis as it acts as reducing agent and alternatively coats the surface of nanoparticles while synthesis and thereby maintaining uniform size and dispersibility. Powder X-ray diffraction（XRD） and magnetic measurements showed that the sample is cubic spinel and superparamagnetic at room temperature. Raman spectra confirmed the formation of the Mg0.8Mn0.2Fe2O4 nanoparticles.The nanoparticles exhibit very good stability in water due to in situ coating with DEG molecules.
基金Project supported by the Education Department of Yunnan,China(Grant No.2015Y103)
文摘Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ phosphors were synthesized by solid-state reaction technique. The crystalline phase and luminescence performances of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ were observed by X-ray powder diffractometer（XRD）, transmission electron microscope（TEM）, photoluminescence spectrometer and brightness meter, respectively. The addition of Ag~＋ can diminish in the crystal particle sizes of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）. Because Ag＋ can reduce the concentration of the undesirable defects in the phosphor, luminescence intensity of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ is 2.3 times as high as that of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）at the same preparation condition. The effect of Ag＋ on the persistent afterglow properties is to deepen the energy storage traps and enhance the energy transfer efficiency from Ca_（0.9）Mg_（0.1）TiO_3 to Pr^（3＋）. The persistent afterglow properties of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ are better than those of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋） at the same preparation condition. In conclusion,Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ phosphor with molar ratio of Ag~＋to Pr^（3＋） 3：1 obtained at 900 ℃ for 4 h exhibits the optimal photoluminescence performances.
文摘Amorphous structure generated by high-energy ball miller(BM)is often used as a precursor for generating nanocomposites through controlled devitrification.The amorphous forming composition range of ternary Al-Cu-Zr system was calculated using the extended Miedema’s semiempirical model.Eleven compositions of Al-Cu-Zr system showed a wide range of negative enthalpy of mixing(-ΔH^(mix))and amorphization(-ΔH^(amor))among the constituent elements was selected for synthesis by BM.They yielded either nanocomposites of partial amorphous and crystalline structure or no amorphous phase at all in the as-milled condition.The Al_(88)Cu_(6)Zr_(6) alloy with relatively small negativeΔH^(mix)(-0.4 kJ/mol)andΔH^(amor)(-14.8 kJ/mol)became completely amorphous after 120 h of milling.
文摘The growth mechanisms of high temperature Yttrium- and Bismuth-based-superconductors were investigated at nanoscale. We started with studying the growth relationships among the three phases of Bi-2201, Bi-2212, and Bi-2233, and then extended to another growth mechanism of Bi-2223 and the growth of yttrium-based high-temperature nanosuperconductors （nano-YBCO）. A time dependence of growth experiment was performed. In this experiment, the Bi-based superconductors grew within different sintering periods, and its three phases were determined by X-ray diffraction. And then, a time dependence of growth model was suggested to explain the experimental facts. With this model, governing equations were derived to quantitatively describe the growth and decomposition mechanisms during sintering period. The results calculated from the derived equations were well in agreement with the experimental data. We also suggested an alternative growth mechanism for the Bi-2223 phase, which was supported by an observation of transmission electron microscopy （TEM）. The nano-YBCO also grew, and their orthorhombic crystal structures were determined by the TEM. The superconducting properties of Bi-2223 were investigated by the measurements of ac magnetic susceptibility. It is expected that the derived equations will fit the alternative experimental growth mechanism of the Bi-2223 phase and the nano-YBCO growth mechanism, too.
