Broken particle-hole symmetry at atomically flat a-axis YBa2Cu3O7-delta interfaces

We have studied quasiparticle tunneling into atomically flat a-axis films of YBa(2)Cu(3)O(7-delta) and DyBa(2)Cu(3)O(7-delta) through epitaxial CaTiO3 barriers. The junction heterostructures were grown by oxide molecular beam epitaxy and were carefully optimized using in situ monitoring techniques, resulting in unprecedented crystalline perfection of the superconductor-insulator interface. Below T(c), the tunneling conductance shows the evolution of a large unexpected asymmetrical feature near zero-bias. This is evidence that superconducting YBCO crystals, atomically truncated along the lobe direction with a titanate layer, have intrinsically broken particle-hole symmetry over macroscopically large areas.     

Energy distribution of electrons emitted from Al-Al2O3-Al system

On sandwich cathodes of the Al-Al₂O₃-Al structure were measured both the VA characteristics of leakage and emission currents and the distribution of emitted electrons according to a normal energy componentN(W _x ) for various voltages thicknesses of dielectric and upper metal films, and various voltages superimposed on cathode (leakage voltage). On the basis of experimental dependences obtained, the influence of single parts of the system on the transported electrons has been discussed. Three groups of distribution ofN(W _x ) were found differing in their form on the one hand and in their position in the energy band diagram of the studied system, on the other one. The dependence of the distribution width and the position of its maximum on the thickness of the dielectric layer and electric field intensity was followed. To describe the processes in a dielectric layer a model assuming the random collision processes has been applied. All three groups of measured distributions may be expressed by a single equation of the typeN(W _x )=N ₀(W _x ). P(z). D(W), except a small number of cases where the influence of the upper electrode barrier due to higher voltages on cathode is not taken into account and thus theD(W) term need not be considered.     

Effect of oxygen vacancies on adhesion at the Nb/Al2O3 and Ni/ZrO2 interfaces

The atomic and electronic structures of the Nb/Al₂O₃(0001) and Ni/ZrO₂(001) interfaces are calculated using density-functional theory. The formation energy of oxygen vacancies is estimated in bulk materials and in surface layers and interfaces for different uppermost atomic layers of oxide surfaces. The work of separation of metal films from oxide surfaces is determined. The effect of oxygen vacancies on the bonding of transition metals to atoms of a substrate determining adhesion at the metal-oxide interfaces is discussed. It is shown that the Nb(Ni)-O interaction at the interfaces weakens in the presence of surface oxygen vacancies.     

Subsolidus phase relation in the Bi2O3-Fe203-La2O3 system

Bismuth-containing semiconductor material is a hot topic in photocatalysts because of its effective absorption under the visible light. In this paper, we expect to explore a new bismuth-based photocatalyst by studying the subsolidus phase relations of the Bi2O3-Fe2O3-La2O3 system. The X-ray diffraction data shows that in this ternary system the ternary compound does not exist, while seven binary compounds （including one solid solution series Bi1-xLaxO1.5 with 0.167 〈 x 〈 0.339） are obtained and eight compatibility triangles are determined.     

Nonstoichiometric interfaces and Al2O3 adhesion with Al and Ag

We have determined the relative stability of stoichiometric, oxygen-rich, and aluminum-rich Al/Al 2O (3) and Ag/Al 2O (3) interfaces from first principles. Stable structures vary significantly with oxygen chemical potentials. Computed works of adhesion agree reasonably well with sessile drop experimental values, including correlation with measured oxygen chemisorption effects on Ag. The ordering of predicted bond energies of the interfaces, ceramics, and metals seems consistent with monotonic and fatigue fracture experiments.     

Phonon kinetics in solid solutions of ceramics in the ZrO2-Y2O3-MgO-Al2O3 system

The propagation of weakly nonequilibrium phonons is studied in ceramics based on ZrO₂-Y₂O₃-MgO-Al₂O₃. Under the assumption of a large dispersion in the ceramic grain sizes, the characteristics of phonon scattering are studied as a function of the temperature and duration of isothermal annealing of the samples and the contribution of the intergrain boundaries to the phonon kinetics is isolated. Fiz. Tverd. Tela (St. Petersburg) 39, 1091–1093 (June 1997)     

Energy migration in a quasi-two-dimensional system: Eu2O2SO4

Energy transfer processes in the system (Gd_1−xEu_x)₂O₂SO₄ (0 < x ⩽ 1) are reported. It is shown that concentration quenching due to energy migration occurs down to the lowest temperatures if x > 0.2. At low temperatures the characteristics of the energy migration processes can be explained using a two-dimensional migration model. The two-dimensional migration behaviour is probably due to a superexchange interaction in the europium layers. The occurrence of pair-absorption lines in the excitation spectra of the concentrated samples can be explained in terms of the same interactions     

Energy levels and interaction between Eu3+-ions at lattice sites of symmetryC 2 and symmetryC 3i in Y2O3

Besides the known energy levels of Eu³⁺ at lattice sites of symmetryC ₂ in Y₂O₃, some transitions of this ion at lattice sites of symmetryC _3i in the same host crystal have been found and it was possible to construct the energy level scheme in part. Evidence for an energy transfer from Eu³⁺(C _3i ) to Eu³⁺(C ₂) is given, the strength of which is measured as a function of the Eu₂O₃ concentration. The results lead to the assumption of a fixed distanceR ₀ for the interaction responsible for the energy transfer. A temperature-independent value ofR ₀=8.7 Å was found. The full explanation of the underlying quantum mechanical mechanism requires further experiments.     

Y2O3纳米晶中两种格位的Eu3+之间的能量传递

讨论了Eu^3 :Y2O3纳米晶在低温下的发光性质。比较了不同颗粒尺寸的Y2O3纳米晶中Eu^3 离子的发射光谱,根据不同温度下的激发谱,分析了处于Y2O3纳米晶中C2和C3i两种格位的激发峰强度随温度的变化,选择激发了不同格位的孤立的Eu^3 离子和处于相邻格位（C3i-C2)的Eu^3 离子对,结果表明,相邻Eu^3 离子对的能量传递速率比孤立的Eu离子之间的能量传递速率快,分析了纳米Eu^3 :Y2O3中猝灭浓度提高的原因。     

Y2O3-Eu2O3-SnO2三元系固相线下相关系及其发光性质研究

采用固态反应法及改良固态反应法合成了一系列Y2O3-Eu2O3-SnO2体系中的试样,利用X射线粉末衍射法测定了Y2O3-Eu2O3-SnO2三元系固相线下的相关系.结果表明,Y2O3-Eu2O3二元系和Eu2Sn2O7-Y2Sn2O7赝二元系形成连续固溶体.对于(Y1-xEux)2Sn2O7,最强的发光峰位置在590 nm附近,源于Eu3+的5 D0-7 F1的磁偶极跃迁.对于(Y1-xEux)2O3,最强峰的位置在611 nm附近,是由Eu3+的5 D0-7 F2的电偶极跃迁引起的.激发光谱表明,与(Y1-xEux)2O3相比,(Y1-xEux)2Sn2O7的电荷迁移带向低能方向移动.Eu3+在化合物中所处的晶体学位置决定了其光谱特征.     

An Ab initio study of reactions in the H3BO3/B2O3/H2O system

The H₃BO₃ ? HBO₂ + H₂O, HBO₂ + HBO₂ ? (HBO₂ · HBO₂) complex, and (HBO₂ · HBO₂) ? B₂O₃ + H₂O reactions of forward and reverse conversion of H₃BO₃ into B₂O₃ and the (HBO₂ · HBO₂) ? (HBO₂)₂ reactions of forward and reverse transformation of the complex into a fairly stable dimer (HBO₂)₂ were studied ab initio at the MP2/6-31+G*//6-31+G* level. The transition state method and calculated equilibrium constants were used to determine forward and reverse reaction constants.     

Heat capacity of oxides in the Bi2O3-SiO2 system

The high-temperature heat capacity of Bi₄Si₃O₁₂, Bi₂SiO₅, and Bi₁₂SiO₂₀ has been investigated. It has been found that there is a correlation between the specific heat C _p ⁰ (298 K) and the composition of oxides in the Bi₂O₃-SiO₂ system.     

Energy Conversion in Gd2O3 Nanocrystals Doped with Er3+ Ions

Physics of the Solid State - The conversion of the energy absorbed by cubic Gd2O3 nanocrystals doped with Er3+ and codoped with Yb3+ and Zn2+ ions in a temperature range of 95–425 K is...