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通过YBa2Cu3x)SnxO7+y体系样品的结构参数、XPS和Mssbauer谱、电阻-温度关系、氧含量以及热分解温度的综合测量,发现:Sn在该体系中替代了Cu的位置并保持4价状态;在x<0.4范围内Sn替代Cu对晶体结构没有影响,引起Tc的变化也极小;Sn替代Cu使体系的氧含量增加,并明显地影响了Cu的价态,使Cu呈现+3价,实验在结构、氧缺位及电子态方面为认识超导电性的起源提供了一些重要信息,在综合分析实验结果的基础上,本文提出:金属原子与氧原子间的耦合程度决定了体系的超导电性。 相似文献
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In this paper it is reported that the measurement of the bulk positron lifetime as a function of substitution content x in the temperature range from 70 to 220K was performed in two high-Tc superconducting systems, Y1-xCaxBa2Cu3-xFexO7-δ and Y1-xCaxBa2Cu3O7-δ. It was found that τB of both systems decreases significantly with x and the temperature dependence of τB is very weak in normal state. In lower temperature region (Tc), a dramatic x-dependent temperature variation of τB was observed in the Ca-substituted system: from a decrease of τB with decreasing T to an increase of τB. With increasing x, the temperature dependence of τB remains weak in the Ca- and Fe- substituted systems. Compared with the experimental data of positron lifetime in other substituted systems and the calculation of the positron density distribution, the authors suggest that positron bulk lifetime spectra behaviour can be interpreted by the physical model based on the transfer of electron density between the CuO2 planes and Cu-O chains. Therefore, the study of positron lifetime spectra provides a useful means to detect the local charge density and to study the correlation between the electronic structure and the high-Tc superconductivity. 相似文献
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Twenty pure elemental metal samples have been studied with a coincidence Doppler broadening system (CDB). The results show the relationship between the CDB spectra and the electronic structure of these samples. The experimental results are compared to simple theoretical predictions, which show that the high-momentum part of the Doppler-broadening spectra can be used to distinguish different elements. 相似文献
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The defect changes in 6H-SiC after annealing and 10MeV electron irradiation have been studied by using a variable-energy positron beam.It was found that after annealing,the defect concentration in n-type 6H-SiC decreased due to recombination with interstitials.When the sample was annealed at 1400℃ for 30 min in vacuum,a 20-nm thickness Si layer was found on the top of the SiC substrate,this is a direct proof of the Si atoms diffusing to surface when annealed at high temperature stages.After 10MeV electron irradiation,for n-type 6H-SiC,the S parameter increased from 0.4739 to 0.4822,and the relative positron-trapping rate was about 27.878 times of the origin sample,this shows that there are some defects created in n-type 6H-SiC.For p-type 6H-SiC,it is very unclear,this may be because of the opposite charge of vacancy defects. 相似文献