We performed a first-principles study of the electronic, elastic, and thermal properties of the rareearth hexaboride CeB6 using the local density approximation （LDA） in consideration of the effective onsite Coulomb ...We performed a first-principles study of the electronic, elastic, and thermal properties of the rareearth hexaboride CeB6 using the local density approximation （LDA） in consideration of the effective onsite Coulomb parameter Ueff. To systemically evaluate the effect of Ueff on the structure of the material, the dependences of the lattice parameter a0 and bulk modulus B on Ueff were examined in the framework of the LDA＋U and GGA（PBE）＋U scheme. We obtained a lattice constant a0, elastic constants Cij, and a bulk modulus B at 0 K and 0 GPa that were in good agreement with the experimental results and other theoretical findings. We focused on the electronic structure by analyzing the variation of the density of states with different Ueff values and pressures, which indicates the metallic characteristic of CeB6. Interestingly, the effect of high pressure was similar to that of increasing Ueff, as the peaks at the bottom of the conduction band moved to the high-energy region in both cases. The elastic constants Cij, bulk modulus B, shear modulus G, Young＇s modulus E, shear-sound velocity Vs, and longitudinal-sound velocity VL were calculated from 0 to 120 GPa. Additionally, the Debye temperature D and elastic Debye temperature E were systematically calculated using the thermodynamic methods in the range of 0-100 GPa. This research may provide a comprehensive understanding of the Kondo compound CeB6 and similar rare-earth hexaborides.展开更多
CeB6 powders were prepared by high-temperature self-propagating synthesis （SHS） in which CeO2, B203 and Mg were taken as reactants. The adiabatic temperature and dynamics of SHS reactions were investigated. The SHS ...CeB6 powders were prepared by high-temperature self-propagating synthesis （SHS） in which CeO2, B203 and Mg were taken as reactants. The adiabatic temperature and dynamics of SHS reactions were investigated. The SHS reaction products and leached products were characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results indicated that the adiabatic temperature of Mg-B2Oa-CeO2 reaction system was rather higher than 1800 K to make the reaction propagate by itself, and the apparent activation energy （Ea） and reaction order （n） of exothermic peak on Mg-BzO3-CeO2 differential scanning calorimetry （DSC） curve were 23.03 kJ/mol and 1.31, respectively. The apparent activation energy was lower, so the reaction occurred easily. The SHS products consisted of MgO, CeB6 and little MgaB2O6. The leached products consisted of single CeB6 phase and its purity was higher than 99.0%, and the average particle sizes of CeB6 were smaller than 150 nm.展开更多
We presented a field electron emission measurement of single crystalline CeB6 nanowires.The nanowires exhibited a low turn-on electric field(7.6 V/μm at 10 μA/cm2),and the deviation of Fowler-Nordheim(F-N) plots fro...We presented a field electron emission measurement of single crystalline CeB6 nanowires.The nanowires exhibited a low turn-on electric field(7.6 V/μm at 10 μA/cm2),and the deviation of Fowler-Nordheim(F-N) plots from straight line was observed in field electron emission measurements.The field enhancement factors were obtained by separate straight line fitting.The nonlinearity in the F-N plots may be attributed to the non-uniform field electron emission of CeB6 nanowires.The field emission properties of the ...展开更多
High temperature self-propagating synthesis （SHS） process is very rapid, the reaction process becomes un-controlled after the SHS reaction is ignited. So the initial reaction conditions will have great effects on ph...High temperature self-propagating synthesis （SHS） process is very rapid, the reaction process becomes un-controlled after the SHS reaction is ignited. So the initial reaction conditions will have great effects on phase compositions and microstructures of reaction products. In this paper, the effects of the proportioning amount of Mg on the yield ratio and particle sizes of CeB6 were studied. The SHS reaction products and leached products were characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results indicated that the SHS products consisted of MgO, CeB6 and little Mg3B206. The single CeB6 phase was contained after the SHS reaction products were leached. The purity of CeB6 was higher than 99.0 mass%, and the minimum particle sizes of CeB6 were within 30-70 nm. When the propor- tioning amount of Mg was 25% more than the theoretic amount, the yield of CeB6 was 68.68%. The antioxidant ability of CeB6 was rather stronger, which was oxidized step by step, and the initial oxidation temperature was 750 ℃ which indicated that it had good high temperature stability. The apparent activation energies of oxidation reactions of CeB6 were 200.09 and 312.10 kJ/mol, respectively, and reaction orders were 0.69 and 0.40, respectively.展开更多
基金Acknowledgements The authors would likc to thank the support by the National Natural Science Foundation of China （Grant No. 11204192）. We also acknowledge the support for the computational resources by the State Key Laboratory of Polymer Materials Engineering of China in Sichuan University.
文摘We performed a first-principles study of the electronic, elastic, and thermal properties of the rareearth hexaboride CeB6 using the local density approximation （LDA） in consideration of the effective onsite Coulomb parameter Ueff. To systemically evaluate the effect of Ueff on the structure of the material, the dependences of the lattice parameter a0 and bulk modulus B on Ueff were examined in the framework of the LDA＋U and GGA（PBE）＋U scheme. We obtained a lattice constant a0, elastic constants Cij, and a bulk modulus B at 0 K and 0 GPa that were in good agreement with the experimental results and other theoretical findings. We focused on the electronic structure by analyzing the variation of the density of states with different Ueff values and pressures, which indicates the metallic characteristic of CeB6. Interestingly, the effect of high pressure was similar to that of increasing Ueff, as the peaks at the bottom of the conduction band moved to the high-energy region in both cases. The elastic constants Cij, bulk modulus B, shear modulus G, Young＇s modulus E, shear-sound velocity Vs, and longitudinal-sound velocity VL were calculated from 0 to 120 GPa. Additionally, the Debye temperature D and elastic Debye temperature E were systematically calculated using the thermodynamic methods in the range of 0-100 GPa. This research may provide a comprehensive understanding of the Kondo compound CeB6 and similar rare-earth hexaborides.
基金supported by National Natural Science Foundation of China(51002025,50644016,50874027)
文摘CeB6 powders were prepared by high-temperature self-propagating synthesis （SHS） in which CeO2, B203 and Mg were taken as reactants. The adiabatic temperature and dynamics of SHS reactions were investigated. The SHS reaction products and leached products were characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results indicated that the adiabatic temperature of Mg-B2Oa-CeO2 reaction system was rather higher than 1800 K to make the reaction propagate by itself, and the apparent activation energy （Ea） and reaction order （n） of exothermic peak on Mg-BzO3-CeO2 differential scanning calorimetry （DSC） curve were 23.03 kJ/mol and 1.31, respectively. The apparent activation energy was lower, so the reaction occurred easily. The SHS products consisted of MgO, CeB6 and little MgaB2O6. The leached products consisted of single CeB6 phase and its purity was higher than 99.0%, and the average particle sizes of CeB6 were smaller than 150 nm.
基金supported by the NSFC Grant (50972046) supported through NSFC Committee of ChinaScience and Technology Foundation supported through the Science and Technology Bureau of Guangdong Government
文摘We presented a field electron emission measurement of single crystalline CeB6 nanowires.The nanowires exhibited a low turn-on electric field(7.6 V/μm at 10 μA/cm2),and the deviation of Fowler-Nordheim(F-N) plots from straight line was observed in field electron emission measurements.The field enhancement factors were obtained by separate straight line fitting.The nonlinearity in the F-N plots may be attributed to the non-uniform field electron emission of CeB6 nanowires.The field emission properties of the ...
基金supported by National Natural Science Foundation of China (51002025)National High Technology Research and Development Program of China(863 Program) (2010AA03A405)National Science and Technology Support Plan of China during the 12th Five-Year Plan (2012BAE01B02)
文摘High temperature self-propagating synthesis （SHS） process is very rapid, the reaction process becomes un-controlled after the SHS reaction is ignited. So the initial reaction conditions will have great effects on phase compositions and microstructures of reaction products. In this paper, the effects of the proportioning amount of Mg on the yield ratio and particle sizes of CeB6 were studied. The SHS reaction products and leached products were characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results indicated that the SHS products consisted of MgO, CeB6 and little Mg3B206. The single CeB6 phase was contained after the SHS reaction products were leached. The purity of CeB6 was higher than 99.0 mass%, and the minimum particle sizes of CeB6 were within 30-70 nm. When the propor- tioning amount of Mg was 25% more than the theoretic amount, the yield of CeB6 was 68.68%. The antioxidant ability of CeB6 was rather stronger, which was oxidized step by step, and the initial oxidation temperature was 750 ℃ which indicated that it had good high temperature stability. The apparent activation energies of oxidation reactions of CeB6 were 200.09 and 312.10 kJ/mol, respectively, and reaction orders were 0.69 and 0.40, respectively.
