3 Cr3 Mo3 VNb 在热冲孔中的应用研究

高合金钢热冲孔冲头寿命关系到模具与产品成本、生产效率、自动化设备的使用,因此,应注重冲头的选材、材料制备与冲头制造工艺。 用 3 Cr3Mo3 VNb 作为高合金钢热冲孔冲头,为提高模具寿命,在材料制备上,优化了成分,采用电渣重熔冶炼,减少杂质,毛坯锻造两次,用大锻造比锻造,冲头热处理用真空炉,三次回火,热处理硬度取 HRC42 ~ 46 ,冲头表面处理采用镀铬工艺,开展了热冲孔工艺试验。 结果表明,用3 Cr3Mo3 VNb 可使冲孔冲头寿命平均达到 800 件以上。     

Exchange bias in LaNiO3-LaMnO3 superlattices

The wide spectrum of exotic properties exhibited by transition-metal oxides stems from the complex competition between several quantum interactions. The capacity to select the emergence of specific phases at will is nowadays extensively recognized as key for the design of diverse new devices with tailored functionalities. In this context, interface engineering in complex oxide heterostructures has developed into a flourishing field, enabling not only further tuning of the exceptional properties of these materials, but also giving access to hidden phases and emergent physical phenomena. Here we demonstrate how interfacial interactions can induce a complex magnetic structure in a non-magnetic material. We specifically show that exchange bias can unexpectedly emerge in heterostructures consisting of paramagnetic LaNiO3 (LNO) and ferromagnetic LaMnO3 (LMO). The observation of exchange bias in (111)-oriented LNO-LMO superlattices, manifested as a shift of the magnetization-field loop, not only implies the development of interface-induced magnetism in the paramagnetic LNO layers, but also provides us with a very subtle tool for probing the interfacial coupling between the LNO and LMO layers. First-principles calculations indicate that this interfacial interaction may give rise to an unusual spin order, resembling a spin-density wave, within the LNO layers.     

Phase equilibria in the system LaMnO3 + δ-SrMnO3-LaFeO3-SrFeO3 − d

We have revealed the formation of a continuous series of orthorhombic LaMn_{1 ? y} Fe_yO₃ solid solutions (0<y<1); La_{1 ? x} Sr_xFeO₃ solid solutions in the composition range 0 < x ≤ 0.8, with an orthorhombic structure at 0 < x ≤ 0.6 and a cubic structure at 0.6 < x ≤ 0.8; and a tetragonal SrMn_{1 ? y} Fe_yO₃ phase in the range 0.6 ≤ y ≤ 1. The composition stability limits of the perovskite phase La_{1 ? x} Sr_xMn_{1 ? y} Fe_yO₃ have been determined, and the 1100°C isotherm of the La₂O₃-SrO-Mn₃O₄-Fe₂O₃ system in air has been constructed.     

高质量钙钛矿单晶CH3NH3PbI3研究进展

有机-无机钙钛矿材料因为具有光谱吸收范围宽、缺陷密度低、载流子复合率低等非常优良的光电性能吸引了广泛关注, 掀起了钙钛矿材料研究热潮。近年来杂化钙钛矿型太阳能电池发展迅速, 光电转化效率目前已达到22.1%, 展现出极大的应用潜力。与多晶薄膜相比, 单晶具有极低的缺陷密度和极少的界面缺陷。多个课题组成功培养出大尺寸钙钛矿单晶, 发现钙钛矿单晶材料具有比其他薄膜多晶材料更好的光响应特性, 是设计制备光伏器件的理想材料。在各类钙钛矿材料中, CH₃NH₃PbI₃是研究和应用最广泛的一类钙钛矿材料。本文主要针对近年来CH₃NH₃PbI₃单晶材料的研究制备进行综述, 介绍了CH₃NH₃PbI₃单晶材料的结构及性能, 重点总结了CH₃NH₃PbI₃单晶材料生长制备方法和应用, 并对其发展趋势进行了展望。     

Phase equilibria in the system BaTiO3-BaGeO3

The system BaTiO₃-BaGeO₃ has been investigated by DTA, metallographic and X-ray diffraction methods. A number of selected samples were also analysed on the electron probe micro-analyser. The system was found to be of the simple binary-eutectic type with partial solid solubility at both ends. The eutectic composition was established as 68±0.5 mol% BaGeO₃ and its melting temperature as 1120±5° C. The solid solubility of BaGeO₃ in BaTiO₃ at 1120°C was found to be 1.8 mol % and that of BaTiO₃ in BaGeO₃ 2.2 mol %. Additions of BaGeO₃ to BaTiO₃ did not appear to cause any change in the temperature of the cubic to hexagonal inversion of BaTiO₃ but the temperature of the tetragonal to cubic inversion was raised slightly with such additions. The transformation temperature of 1180° C for the low- to high-temperature form of BaGe0₃ was not affected by additions of BaTiO₃     

Microwave absorption in NaNbO3-PbTiO3 solid solutions

The microwave absorption spectra of (Na,Pb)(Nb,Ti)O₃ solid solutions have been measured in the frequency range 7.8–11.8 GHz, and the composition dependences of the maximum microwave absorption in the solid solutions have been obtained. It is shown that most of the peaks observed in the composition dependences of microwave absorption are located near morphotropic phase boundaries. The effect of preparation conditions on the absorbing capacity of the solid solutions is analyzed.     

Microwave absorption in SrTiO3-BiCrO3 solid solutions

Data are presented on the electrical conductivity of SrTiO₃-BiCrO₃ solid solutions as a function of temperature and their dielectric permittivity and loss tangent as functions of temperature and frequency. The high dielectric losses in this solid-solution system are shown to be due to relaxation processes. The relaxation behavior of the solid solutions containing 30 and 40 mol % BiCrO₃ is analyzed using the frequency dependences of peak permittivity and peak tan δ, and the activation energy of dielectric relaxation is evaluated. The relaxation process is assumed to be associated with the thermal motion of the ions in the A site. The loss tangent is calculated in a broad frequency range, from 10 MHz to 2.5 GHz.     

3He-3He quasiparticle interaction in3He-4He mixtures under pressure

Based on our recent phase separation curve of³He-⁴He solution at elevated pressures, we propose new³He-³He quasiparticle interaction potentials, which reproduce the existing experimental results pretty well except for³He effective mass under pressure.     

Up-conversion fluorescence of Tm3+ and Gd3+ in Yb3+/Tm3+ co-doped Gd2O3 nanocrystals

Through a co-precipitation method Gd(OH)3:20%Yb3+, 1%Tm3+ nanorods were synthesized. After sintered at 900 degrees C for 1 h in air, the as-prepared Gd(OH)3:20%Yb3+, 1%Tm3+ nanorods were converted into Gd2O3:20%Yb3+, 1% Tm3+ nanocrystals. Crystalline phases, sizes, and morphologies of the two samples were characterized by X-ray diffraction and field emission scanning electron microscope. The up-conversion (UC) fluorescence spectra of the Gd2O3:20%Yb3+, 1%Tm3+ nanocrystals were recorded by using a fluorescence spectrophotometer with a 980 nm continuous wave laser diode as excitation source. The nanocrystals not only present characteristic blue and ultraviolet (UV) UC emissions of activated Tm3+, but also show UV UC emissions of host Gd3+. The experimental study suggests that the excitation power has great effects on UC fluorescence properties and the energy transfer from Tm3+ to Gd3+ is very efficient.     

Optical transition probability of Nd3+ ion in α-Ba3Y(BO3)3 crystal

Optical absorption and emission intensities have been investigated for the Nd³⁺ ion in α-Ba₃Y(BO₃)₃ crystal. Based on the Judd-Ofelt theory the spectral parameters were obtained. The intensity parameters Ω_λ are: Ω₂ = 0.62 × 10^–20 cm², Ω₄ = 0.90 × 10^–20 cm², Ω₆ = 1.06 × 10^–20 cm². The radiative lifetime is 1104 μs, and quantum efficiency is equal to 6.9%. The fluorescence branching ratios are: β₁ (0.88 μm) = 0.4050, β₂ (1.06 μm) = 0.4897, β₃ (1.35 μm) = 0.1000 and β₄ (1.88 μm) = 0.0053. Electronic Publication     

Perovskite phase formation in the PbMg1/3Nb2/3 O3-PbZrO3-PbTiO3 system by the columbite route

The reaction mechanism of PbMg_1/3Nb_2/3O₃-PbZrO₃-PbTiO₃ (PMN-PZT) perovskite phase prepared by the columbite route has been studied in the temperature range from 600 to 800 °C. The effects of heating and cooling rate during the calcination of 3PbO +MgNb₂O₆+PZT powder mixtures have also been investigated. Nearly pure perovskite phase, 0.9 PMN-0.1 PZTsolid solution with no pyrochlore phase, as determined by X-ray diffraction, could be prepared at 800 °C for 2 H. From DTA/TGA, dilatometry and XRD data the reaction mechanism of PMN-PZT solid solution formation could be divided into three steps: (i) decomposition of columbite (MgNb₂O₆) by reacting with PbO at 350 to 600 °C (ii) the formation of a B-site-deficient pyrochlore phase Pb₂Nb_1.33Mg_0.17O_5.50 at close to 650 °C, and (iii) the formation of perovskite phase PMN-PZT solid solution from the reaction of Pb₂Nb_1.33Mg_0.17O_5.50 pyrochlore phase with MgO and PZT above 650 °C.     

γ-Radiolysis of Polyynes in Heptane

The polyynes in heptane solution were γ-radiolyzed at a total dose of 150, 300 and 600 kGy. After radiolysis the products were analyzed by electronic absorption spectroscopy, by HPLC (liquid chromatography) and by FT-IR spectroscopy. Even at 150 kGy the polyynes disappear completely from the solution and the chromatographic analysis shows that the acetylenic chains undergo fragmentation, addition and crosslinking reactions with other chains and with solvent. The oxidative interference from air has been detected by FT-IR.     

Measurement of the γ-anisotropy in

The study of the radiative neutron capture by protons, n+p→d+γ, provides valuable information about the nucleon–nucleon interaction. So far, no experimental value has existed for the γ-anisotropy which may appear if neutrons and protons both are polarised. A non-vanishing γ-anisotropy η is a clear-cut signal for the existence of transitions ³S₁→ ³d₁ from the triplet initial state to the ground state of the deuteron. We report the first measurement of this observable. The result is η=(1.0±2.5)×10⁻⁴ at 50.5% polarisation of neutrons and protons.     

Martensitic transformations in V3Ga and Nb3Al

It is shown by low-temperature heat capacity measurements using ac technique that martensitic transformation in small samples of V₃Ga and Nb₃A1 can be prevented by covering them nearly completely with copper plating.     

Switchable induced polarization in LaAlO3/SrTiO3 heterostructures

Demonstration of a tunable conductivity of the LaAlO(3)/SrTiO(3) interfaces drew significant attention to the development of oxide electronic structures where electronic confinement can be reduced to the nanometer range. While the mechanisms for the conductivity modulation are quite different and include metal-insulator phase transition and surface charge writing, generally it is implied that this effect is a result of electrical modification of the LaAlO(3) surface (either due to electrochemical dissociation of surface adsorbates or free charge deposition) leading to the change in the two-dimensional electron gas (2DEG) density at the LaAlO(3)/SrTiO(3) (LAO/STO) interface. In this paper, using piezoresponse force microscopy we demonstrate a switchable electromechanical response of the LAO overlayer, which we attribute to the motion of oxygen vacancies through the LAO layer thickness. These electrically induced reversible changes in bulk stoichiometry of the LAO layer are a signature of a possible additional mechanism for nanoscale oxide 2DEG control on LAO/STO interfaces.     

The AB Transition in Superfluid $$^3$$ 3 He

Journal of Low Temperature Physics - The discovery of superfluidity in $$^3$$ He in 1971, published in 1972, [1, 2] has influenced a wide range of investigations that extend well beyond fermionic...     

Ultraviolet upconversion fluorescence of Er3+ in Yb3+/Er3+-codoped Gd2O3 nanotubes

Under 980 nm excitation, room-temperature ultraviolet (UV) upconversion (UC) emissions of Er3+ from the 4G(9/2), 2K(13/2), and 2P(3/2) states were observed in Gd2O3:Yb3+/Er3+ nanotubes, which were synthesized via a simple wet-chemical route at low temperature and ambient pressure followed by a subsequent heat treatment at 800 degrees C. The experimental results exhibited that these UV emissions came from four-photon UC processes. In the Gd2O3:Yb3+/Er3+ nanocrystals, the energy transfers (ETs) from Yb3+ to Er3+ played important roles in populating the high-energy states of Er3+ ions. This material provides a possible candidate for building UV compact solid-state lasers or fiber lasers.     

SrTiO3双功能陶瓷中CaTiO3掺杂的研究

研究了ＣａＴｉＯ３掺杂对ＳｒＴｉＯ３电容－压敏陶瓷材料微观结构和电性能的作用。ＸＲＤ和ＩＲ分析结果表明过量Ｃａ＾２＋掺杂使得晶格结构的对称性和分子规整度降低。电性能测试表明Ｃａ＾２＋掺杂利于降低烧结后的表观电阻率,压敏电压和表观介电常数随ＣａＴｉＯ３含量的增大分别表现出量小、最大值。