Anomalous magnetic properties of an iron film system deposited on fracture surfaces of α-Al2O3 ceramics

An iron film percolation system is fabricated by vapour-phase deposition on fracture surfaces of α-Al2O3 ceramics. The zero-field-cooled （ZFC） and field-cooled （FC） magnetization measurement reveals that the magnetic phase of the film samples evolve from a high-temperature ferromagnetic state to a low-temperature spin-glass-like state, which is also demonstrated by the temperature-dependent ac susceptibility of the iron films. The temperature dependence of the exchange bias field He of the iron film exhibits a minimum peak around the temperature T=5 K, which is independent of the magnitude of the cooling field Hcf. However, for T 〉 10K, （1） He is always negative when Hcf=2kOe and （2） for Hcf= 20 kOe （1Oe≈80 A/m）, He changes from negative to positive values as T increases. Our experimental results show that the anomalous hysteresis properties mainly result from the oxide surfaces of the films with spin-glass-like phase.     

脉冲形成线用CaO-TiO2-Al2O3基介质陶瓷介电性能

设计了一种脉冲形成线用新型CaO-TiO2-Al2O3基介质陶瓷体系,采用传统固相法通过优化组分和制备工艺,调控材料的微结构,获得了介电性能优异的介质陶瓷。其介电常数在15~35之间可调,介电损耗小于0.002,频率稳定性好。在厚度为1 mm时,介电强度高达50 kV/mm。研究了厚度对CaO-TiO2-Al2O3基介质陶瓷介电强度的影响规律,当厚度从1 mm减小到0.1 mm时,介电强度呈非线性增大,从50 kV/mm（1 mm厚样品）提高到92 kV/mm（0.1 mm厚样品）,可见,CaO-TiO2-Al2O3基介质陶瓷的电击穿与其机械损坏具有相似性。结合CaO-TiO2-Al2O3基介质陶瓷的化学组分和微观结构,CaO-TiO2-Al2O3基介质陶瓷优越的电击穿特性可以用弱点击穿理论解释。     

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.     

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)     

Pyrolysis of molybdenum peroxides in γ-Al2O3

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 48, No. 6, pp. 994–998, June, 1988.     

Mutual relation of leakage and emission currents in the Al-Al2O3-Al system

In the present paper the analysis of VA characteristics of the leakage current determined experimentally for the Al-Al₂O₃-Al system is discussed. It is shown that the total leakage current is given by a sum of several local currents from the single places of the dielectric given by various mechanisms acting simultaneously. The tunnel component of the leakage current passes through a part of the dielectric area only. This current component obeys the same regularities holding for the case of emission current of electrons into vacuum. Comparison of the values of applied field intensity obtained for this tunnel component leakage current with the values corresponding to the Fowler-Nordheim equation suggests the assumption of a nonuniform potential distribution in the dielectric, i.e. the existence of a region where the potential drop agrees with the theoretical values and the region of a lower potential drop. Further, the influence of the position of potential barrier and the transmission probability over the top electrode on the emission VA characteristics is shown.     

Formation and Evolution of Carbonate Species in Na-Doped Al2O3 and V2O5-Al2O3

A study is carried out by FT-IR spectroscopy of the carbonate species formed upon interaction of CO₂ with alumina and vanadia-alumina catalysts doped with sodium. It is found that the presence of sodium enhances the ability of the catalyst surface to adsorb CO₂, yielding to carbonate formation. The species formed changes in the presence of vanadium, shifting the ν_COO stretching bands towards higher wavenumbers than those recorded in Na-Al₂O₃ systems.     

SO2-4/Fe2O3-Al2O3纳米固体酸的红外光谱研究

用IR光谱研究了SO4^2-/Fe2O3-Al2O3纳米固体酸在不同焙烧温度下表面结构与酸性的变化，结果表明，当焙烧温度在450－500℃时，双齿螯合配位结构特征谱带齐全，酸性强，小于450℃时，双齿螯合配位特征谱带不齐全，酸性不强，而大于500℃时，随着温度的升高，特性谱带区域宽化，特征峰消失，酸性变弱。此外，从Fe-O纳米颗粒的特征振动带显示可得知，样品的粒径小于30nm。     

Tunneling luminescence of Y2O3 and Sc2O3 ceramics

In the present work we investigate the tunneling luminescence (TL) of Y₂O₃, Y₂O₃:Eu, and Sc₂O₃ ceramics. From an analysis of the decay kinetics of the TL it is established that the recombinational processes are described by a model involving recombination with a complex interaction. In addition, using the method of partial light sums, we show that in the ceramics investigated the mechanisms of TL are the same and the majority of radiation-induced defects in pairs are removed to distances exceeding the radius of effective tunneling transitions with a time constant of 10–100 sec. In the Y₂O₃:Eu ceramics the distances between defects decrease. TL occurs in pairs whose electron component is F-centers that are thermally released at 176 K in the Y₂O₃ ceramics and 200 K in the Sc₂O₃ ceramics. The hole components of tunneling pairs are associated with centers that are thermally released at 110 and 122 K in the Y₂O₃ ceramics and at 121 and 146 K in the Sc₂O₃ ceramics. To whom correspondence should be addressed. I. Franko Lvov State University, 50, Dragomanov Str., Lvov, 290005, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 5, pp. 649–651, September–October, 1999.     

Local trapping sites in Y2O3 and Sc2O3 ceramics

Heat-stimulated luminescence (HSL) of x-ray-irradiated Y₂O₃, Y₂O₃:Eu, and Sc₂O₃ ceramics samples is investigated. An analysis of the form of the elementary contours making the HSL curves shows that recombination processes at the HSL peaks with maxima at 110, 122, 176, 185, 200, and 247 K in Y₂O₃. ceramics and with those at 121, 136, 200, 215, and 221 K in Sc₂O₃ are described in terms of linear kinetics. The spectral composition of the HSL of the ceramic obtained is studied. Some methods are employed to determine the activation energies and frequency factors corresponding to the HSL peaks. It is established that the recombination processes occurring upon release of the trapping sites in the Y₂O₃ and Sc₂O₃ ceramic samples are conditioned by diffusion-controlled tunneling recombination due to heat-stumulated migration of V_k-centers. L'vov I. Franko State University, 50, Dragomanov St., L'vov, 290005, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 348–353, May–June, 1997.     

Spectroscopic properties of Er3+-doped AlF3-La2O3-Al2O3-SiO2 glasses

Er3+-doped fluoride lanthanum aluminosilicate glasses with compositions of (65- x/2)SiO2 · (25 -and their glass transition temperatures and spectroscopic properties were investigated. The Ω2, Ω4, and Ω6 intensity parameters of glasses were calculated by Judd-Ofelt theory from absorption curves. It was found that glasses transition temperature and melting temperature decreased with the increase of fluoride content in glass, Ω2 decreased gradually with the increase of AlF3 content, but both Ω4 and Ω6 did not increase until AlF3 content increased to 30 mol%. The quantum efficiency of 4I13/2 to 4I15/2 transition of Er3+ ions increases with the increase of AlF3 content in glass. Fluorescent lifetime is longer in glass containing more AlFa content.     

催化精馏专用填料型固体酸SO42-/ZrO2-Al2O3-Al的研究

为了研制催化精馏专用催化剂 ,采用铝阳极氧化法制备了Al2 O3 Al一体型载体 ,并将活性固体超强酸SO42 -/ZrO2 引入到Al2 O3 Al上 ,得到一种新型催化精馏专用填料式固体酸SO42 -/ZrO2 Al2 O3 Al催化剂 .利用XRD、SEM、BET、XPS、NH3 TPD等手段对其进行了表征 .结果表明 ,所制得的阳极氧化铝膜厚为 5 6 μm ,SO42 -/ZrO2 Al2 O3 Al固体酸具有比表面积大、酸强度适中的特点 .XRD结果表明 ,ZrO2 在Al2 O3 Al上处于高度分散状态 .将该固体酸用于乙酸 /乙醇酯化反应中 ,显示出较高的催化活性 ,且稳定性较好     

Accumulation and flow of charge in MOS structures with Al2O3 and SiO2-Al2O3 films on silicon

A expérimental study has been carried out on the processes involved in the accumulation and flow of charge in MOS structures with thin films of Al₂O₃ and SiO₂-Al₂O₃ under various polarization conditions. The activation energy, the frequency factors, the sites of the trapping centers of the polarization charge, and the character of the flow of charge on thermal depolarization have been studied. It is shown that in a structure with a double-layer dielectric, the instability of the charge cannot be explained by the Maxwell-Wagner polarization model in its pure form because of the accumulation of charge in the spatially distributed trapping centers throughout the Al₂O₃ film. The parameters of the traps at the interface between the dielectrics have been determined and the contribution made to the instability of the charge by the migration of ions in these particular structures has been evaluated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 7–14, April, 1978.