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51.
高温高压下CeTbO3合成过程中电阻的动态测试研究 总被引:1,自引:1,他引:0
在0.5 GPa、4.0 GPa的压力下,从室温到800 ℃的温度范围内测量了氧化物CeTbO3、单稀土氧化物Tb4O7、CeO2和摩尔比维4∶1配比的混合物CeO2+Tb4O7等的电阻随温度变化关系。对这四种物质均反映出电阻随温度增加而减小的半导体特征。在压力维0.5 GPa,温度高于600 ℃时发现了混合物CeO2+Tb4O7、氧化物Tb4O7中电阻变化的起伏。X射线衍射谱表明,对应这一电阻变化,在结构上出现了变化。结果分析表明,这一变化与Tb4+→Tb3+的价态变化密切相联。 相似文献
52.
Armando Fernández Guillermet Per Gustafson Mats Hillert 《Journal of Physics and Chemistry of Solids》1985,46(12):1427-1429
It is sometimes advantageous to have an expression for the Gibbs energy, Gm(T,P), from which one can analytically derive an expression for the Heimholtz energy, Fm(T, Vm). Such an expression is suggested for solid substances and it is shown how expressions for other physical properties can be derived from it. 相似文献
53.
考虑到氧化物高温超导体与传统超导体磁性质之间的不同之处,文章从不可逆线的解释,Anderson模型的一种修正方案以及对S-T关系曲线的解释等三个方面对高温超导体的磁通动力学行为作了简要的介绍。 相似文献
54.
D. F. Digor P. Entel V. A. Moskalenko N. M. Plakida 《Theoretical and Mathematical Physics》2006,149(1):1382-1392
We consider the four-band model of high-temperature superconductors with copper
and 4s electrons and oxygen 2p
x
and 2p
y
electrons. We assume that the Coulomb repulsion between the copper 3d electrons is strong. We diagonalize the oxygen subsystem and pass to the Wannier representation for the CuO
2 cluster. We study the properties of a local cell model and find its low-energy states such as the one-particle doublet and
the two-particle singlet and triplet states. We consider the cell fermion delocalization because of their tunneling between
the copper sites. We obtain a system of Dyson-type equations for renormalized one-particle Green’s functions and discuss whether
it can be simplified.
__________
Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 149, No. 1, pp. 99–110, October, 2006. 相似文献
55.
Normal state resistivity and Hall effect are shown to be successfully modeled by a two-band model of holes and electrons that is applied self-consistently to (i) dc transport data reported for eight bulk-crystal and six oriented-film specimens of YBa2Cu3O7?δ, and (ii) far-infrared Hall angle data reported for YBa2Cu3O7?δ and Bi2Sr2CaCu2O8+δ. The electron band exhibits extremely strong scattering; the extrapolated dc residual resistivity of the electronic component is shown to be consistent with the previously observed excess thermal conductivity and excess electrodynamic conductivity at low temperature. Two-band hole–electron analysis of Hall angle data suggests that the electrons possess the greater effective mass. 相似文献
56.
High-temperature annealing of the atomic layer deposition (ALD) of Al2O3 films on 4H-SiC in O 2 atmosphere is studied with temperature ranging from 800℃ to 1000℃. It is observed that the surface morphology of Al2O3 films annealed at 800℃ and 900℃ is pretty good, while the surface of the sample annealed at 1000℃ becomes bumpy. Grazing incidence X-ray diffraction (GIXRD) measurements demonstrate that the as-grown films are amorphous and begin to crystallize at 900℃. Furthermore, C-V measurements exhibit improved interface characterization after annealing, especially for samples annealed at 900℃ and 1000℃. It is indicated that high-temperature annealing in O2 atmosphere can improve the interface of Al2O3 /SiC and annealing at 900℃ would be an optimum condition for surface morphology, dielectric quality, and interface states. 相似文献
57.
The high-temperature phase transition is analyzed according to the DSC of as-cast LaFe11.7 Si1.3 compound and the X-ray patterns of LaFe11.7Si1.3 compounds prepared by high-temperature and short-time annealing. Large amount of 1:13 phase begins to appear in LaFe11.7Si1.3 compound annealed near the melting point of LaFeSi phase (about 1422?K). When the annealing temperature is close to the temperature of peritectic reaction (about 1497?K), the speed of 1:13 phase formation is the fastest. The phase relation and microstructure of the LaFe11.7Si1.3 compounds annealed at 1523?K (5?h), 1373?K (2?h)?+?1523?K (5?h), and 1523?K (7?h) +1373?K (2?h) show that longer time annealing near peritectic reaction is helpful to decrease the impurity phases. For studying the influence of different high-temperature and short-time annealing on magnetic property, the Curie temperature, thermal, and magnetic hystereses, and the magnetocaloric effect of LaFe11.7Si1.3 compound annealed at three different temperatures are also investigated. Three compounds all keep the first order of magnetic transition behavior. The maximal magnetic entropy change ΔSM (T, H) of the samples is 12.9, 16.04, and 23.8?J?kg?1?K?1 under a magnetic field of 0–2?T, respectively. 相似文献
58.
采用高温固相烧结法成功制备了Ba5-3x/2B4O11∶xEu3+(x=0.02~0.22)荧光粉,利用XRD和SEM等对荧光粉进行了结构和形貌表征。 在激发波长为393 nm的条件下,发射峰(596、621、657和706 nm)与Eu3+的5D0-7FJ(J=1,2,3,4)电子跃迁相对应,其中621 nm最强发射峰由Eu3+离子5D0→7F2电偶极跃迁造成。 文章还研究了Eu3+掺杂浓度对Ba5-3x/2B4O11∶xEu3+发光性能的影响,结果表明,荧光粉的发光强度随着Eu3+掺杂量的增加呈现先增大后减小的趋势,Eu3+最佳掺杂量为0.16。 相似文献
59.
采用高温固相法合成了系列Ce~(3+)和Ce~(3+)/Tb~(3+)激活的具有磷灰石结构荧光粉Ba_(10)(PO_4)_6F_2。用X射线衍射(XRD)、扫描电镜(SEM)、激发和发射(PLE和PL)光谱对样品进行了表征分析。研究结果表明:所合成的荧光粉Ba_(10)(PO_4)_6F_2∶Ce~(3+),Tb~(3+)具有氟磷灰石结构,样品微观呈现不规则形貌。荧光粉Ba10-x(PO4)6F2∶x Ce~(3+)的相对发射强度随着x增加而增强,当x=0.09时,荧光强度达到最大。荧光粉Ba_(10)(PO_4)_6F_2∶Ce~(3+),Tb~(3+)的激发光谱为240~330 nm的宽带,发射光谱呈现出Ce~(3+)的5d→4f跃迁紫外光(335和358 nm)发射和Tb~(3+)的4f→4f跃迁绿光(542 nm)发射。光谱特性表明,发光过程中存在Ce~(3+)→Tb~(3+)能量传递,能量传递效率可以达到60%。计算Ce~(3+)和Tb~(3+)的临界距离为0.79 nm,能量传递机理是偶极-偶极交互作用。此外,详细论述了Ce~(3+)和Tb~(3+)之间的能量传递和发光的过程。通过调节Tb~(3+)的掺杂浓度,对荧光粉发光色坐标与Tb~(3+)的掺杂浓度之间的关系也进行了研究,随着Tb~(3+)的掺杂量从0增加0.52,荧光粉Ba_(10)(PO_4)_6F_2∶Ce~(3+),Tb~(3+)的发射光谱色坐标可以从(0.149 4,0.045 1)蓝色区变化到(0.280 1,0.585 3)绿色区。 相似文献
60.
采用高温固相法制备了Sr_3Y(BO_3)_3:xTm~(3+),yDy~(3+)荧光粉,并通过XRD、SEM和荧光光谱仪对样品的物相、微观形貌、发光性能、能量传递机制和CIE色坐标进行了分析。结果表明:Sr_3Y(BO_3)_3:xTm~(3+)荧光粉在监测波长为359 nm时发射蓝光,Tm~(3+)的浓度淬灭点为x=0.08;在Sr_3Y(BO_3)_3:0.08Tm~(3+),yDy~(3+)荧光粉中,随着Dy~(3+)掺杂浓度的增加,Tm~(3+)的发光强度降低而Dy~(3+)发光强度却先增加后降低,Dy~(3+)的浓度淬灭点为y=0.1;通过改变Dy~(3+)掺杂浓度或改变激发光的波长,均可实现发射光的颜色可调;在Tm~(3+)-Dy~(3+)离子之间存在能量传递。当Dy~(3+)掺杂浓度(物质的量分数)为0.15时能量传递效率达75.14%,能量传递机制为电偶极-电偶极相互作用。 相似文献