Electron conduction associated with the chemical transport of reducing elements in oxide cathode for CRT's application

In the present work, the formation of compounds associated to the diffusion of reducing elements (Mg, Al and W) to the Ni cap surface of oxide cathode has been studied by a new method. This method used two cathodes, one of them is coated and the other is uncoated, to be in an attach-contact mounted in a dummy tube. Different analytical techniques were used for this study: scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX) and I/V electrical measurements. After oxide cathode plus decomposited and activated, Al and Mg doping elements take place during heating to 810 °C (Ni-Br) under a rich controlled Ba/SrO atmosphere through an acceleration life test.It is shown that the chemical transport occurs mainly by a grain boundary mechanism with significant pile-up of Mg compounds. Al and W show a superficial concentrations and distribution.The dc electrical characteristic shows very strong rectifying behaviour through the M-S junction due to the I/V curves, particularly after 144 h acceleration life time. The characteristics are found to be reversible and reproducible, and viewed a rectification ratio (r) of 100. The calculated ideality factor shows a value of n = 9.6, which is evidenced to the tunnelling conduction.The theoretical calculation shows that the interface thickness grows to (∼6 μm) after accelerated the cathode to 1896 h.     

Studies on the activation energy from the ac conductivity measurements of rubber ferrite composites containing manganese zinc ferrite

Manganese zinc ferrites (MZF) have resistivities between 0.01 and 10 Ω m. Making composite materials of ferrites with either natural rubber or plastics will modify the electrical properties of ferrites. The moldability and flexibility of these composites find wide use in industrial and other scientific applications. Mixed ferrites belonging to the series Mn_(1−x)Zn_xFe₂O₄ were synthesized for different ‘x’ values in steps of 0.2, and incorporated in natural rubber matrix (RFC). From the dielectric measurements of the ceramic manganese zinc ferrite and rubber ferrite composites, ac conductivity and activation energy were evaluated. A program was developed with the aid of the LabVIEW package to automate the measurements. The ac conductivity of RFC was then correlated with that of the magnetic filler and matrix by a mixture equation which helps to tailor properties of these composites.     

Effect of WO3 on EPR, structure and electrical conductivity of vanadyl doped WO3·M2O·B2O3 (M=Li, Na) glasses

Glasses with composition xWO₃·(30−x)M₂O·70B₂O₃ (M=Li, Na; 0≤x≤15) doped with 2 mol% V₂O₅ have been prepared using the melt-quench technique. The electron paramagnetic resonance spectra have been recorded in X-band (ν≈9.14 GHz) at room temperature (RT). The spin Hamiltonian parameters, dipolar hyperfine coupling parameter and Fermi contact interaction parameter have been calculated. It is observed that the resultant resonance spectra contain hyperfine structures (hfs) only due to V⁴⁺ ions, which exist as VO²⁺ ions in octahedral coordination with a tetragonal compression in the present glass system. The tetragonality increases with WO₃:M₂O ratio and also there is an expansion of 3d_xy orbit of unpaired electron in the vanadium ion. The study of IR transmission spectra over a range 400-4000 cm⁻¹ depicts the presence of WO₆ group. The DC conductivity (σ) has been measured in the temperature range 423-623 K and is found to be predominantly ionic.     

新型贮存式氧化物阴极寿命机理的初步探讨

对一种新型贮存式氧化物阴极及一种普通氧化物阴极进行了寿命实验,采用XPS分析技术对这两种阴极寿命中不同涂层深度的Ba浓度进行对比分析,结合新型贮存式阴极结构及贮存发射材料的性质对这种阴极的寿命机理进行了探讨.结果表明,新型贮存式氧化物阴极的寿命是普通氧化物阴极的7倍,同时发现新型贮存式氧化物阴极涂层深处保持稳定Ba浓度是其具有长寿命的关键. 关键词： 氧化物阴极 寿命 盈余Ba 贮存发射材料     

Physical foundations of the oxide cathodes

A novel explanation of the low values of work function in case of activated (partly deoxidized) polycrystalline oxides of alkali and alkaline earth metals is offered. Use of the metallic plasma model to the conducting oxides leads to the following values (in eV): 1.00, 1.67, 1.50, 1.44, 1.46 and 1.59 for activated Cs₂O, CaO, SrO, BaO, Y₂O₃ and La₂O₃, respectively. The main reason of low work function of the oxide cathodes is very low density of free electrons in the emitting surface layer.     

Effects of protons and acceptor substitution on the electrical conductivity of La6WO12

Transport properties and non-stoichiometry of La_1−xCa_xW_1/6O₂ and La_1−yW_1/6O₂ (x=0, 0.005, 0.05; y=0.05, 0.1) have been characterized by means of impedance spectroscopy, the EMF-technique, H⁺/D⁺ isotope exchange, and thermogravimetry in the temperature range 300-1200 °C as a function of oxygen partial pressure and water vapor partial pressure. The materials exhibit mixed ionic and electronic conductivities; n- and p-type electronic conduction predominate at high temperatures under reducing and oxidizing conditions, respectively. Protons are the major ionic charge carrier under wet conditions and predominates the conductivity below ∼750 °C. The maximum in proton conductivity is observed for LaW_1/6O₂ with values reaching 3×10⁻³ S/cm at approximately 800 °C. The high proton conductivity for the undoped material is explained by assuming interaction between water vapor and intrinsic (anti-Frenkel) oxygen vacancies.     

Effect of La substitution on conductivity and dielectric properties of Bi1−xLaxFeO3 ceramics: An impedance spectroscopy analysis

Bismuth ferrite (BFO) and La-substituted BFO with composition Bi_1−xLa_xFeO₃ (x=0.05, 0.1 and 0.15) (BLFO_x=0.05-0.15) ceramics were prepared using the solid state reaction route. A structural phase transition from rhombohedral phase to triclinic phase was observed for BLFO_x=0.05-0.15 ceramics. Modulus spectroscopy reveals the deviation of dielectric behavior from ideal Debye characteristics and the dependence of conductivity on ion hopping in BFO and BLFO_x=0.05-0.15 ceramics. The conductivity of the BFO ceramics decreases for La content of 5 mol%, followed by a subsequent increase with 10 and 15 mol% of lanthanum doping. The typical values of the activation energies at high temperature reveal the contribution of short range movement of doubly ionized oxygen vacancies to the conduction process in BFO and BLFO_x=0.05 ceramics. Both short range and long range motion of oxygen vacancies are responsible for large conductivity in BLFO_{x=0.1 and 0.15} ceramics.     

Effect of alkali content on AC conductivity of borate glasses containing two transition metals

Sodium borate glasses containing iron and molybdenum ions with the total concentration of transition ions constant and gradual substitution of sodium oxide (network modifier) by borate oxide (network former) was prepared. Densities, molar volume, DC and AC conductivities are measured. The trends of these properties are attributed to changes in the glass network structure. Their DC and AC conductivity increased with increasing NaO concentration. The increase of AC conductivity of sodium borate glasses is attributed to the chemical composition and the hopping mechanism of conduction. Measurements of the dielectric constant (ε) and dielectric loss (tan δ) as a function of frequency (50 Hz–100 kHz) and temperature (RT—600 K) indicate that the increase in dielectric constant and loss (ε and tan δ) values with increasing sodium ion content could be attributed to the assumption that Fe and Mo ions tend to assume network-forming position in the glass compositions studied.The variation of the value of frequency exponent s for all glass samples as the function of temperature at a definite frequency indicates that the value of s decreases with increasing the temperature which agrees with the correlated barrier-hopping (CBH) model.     

Enhancing the phase stability and ionic conductivity of scandia stabilized zirconia by rare earth co-doping

Effect of co-doping Yb, Gd and Ce in scandia stabilized zirconia (SSZ) on the phase stability, high temperature aging behavior and ionic conductivity was studied. Both binary (10 mol% SSZ) and the ternary (co-doped) compositions were found to be in single cubic phase in the as-processed condition. However, the binary composition exhibited the rhombohedral ‘β’ phase after sintering whereas the ternary compositions remained in the single cubic phase. The sintered pellets were aged at 900 °C for 500 h in air to study the phase stability at high temperature. Transmission electron microscopy revealed that the aged samples of Yb and Gd co-doped compositions contain small amount of the tetragonal phase which resulted in considerable degradation in conductivity (more than 20%). The Ce co-doped sample, on the other hand, was in single cubic phase after aging and this ensured that conductivity reduction was minimal in this composition. The co-doped samples however, showed higher conductivity before and after aging compared to the binary composition. The rhombohedral ‘β’ phase was absent in all the co-doped ternary compositions even after high temperature aging.     

Ionic conductivity and electrochemical stability of poly(methylmethacrylate)-poly(ethylene oxide) blend-ceramic fillers composites

The role of inorganic ceramic fillers namely nanosized Al₂O₃ (15-25 nm) and TiO₂ (10-14 nm) and ferroelectric filler SrBi₄Ti₄O₁₅ (SBT CIT) (0.5 μm) synthesized by citrate gel technique (CIT) on the ionic conductivity and electrochemical properties of polymer blend 15 wt% PMMA+PEO₈:LiClO₄+2 wt% EC/PC electrolytes were investigated. Enhancement in conductivity was obtained with a maximum of 0.72×10⁻⁵ S cm⁻¹ at 21 °C for 2 wt% of SrBi₄Ti₄O₁₅ (SBT CIT) composite polymer electrolyte. The lithium-ion transport number and the electrochemical stability of the composite polymer electrolytes at ambient temperature were analyzed. An enhancement in electrochemical stability was observed for polymer composites containing 2 wt% of SrBi₄Ti₄O₁₅ (SBT CIT) as fillers.     

Experimental measurement of the electrical conductivity of pyroxenite at high temperature and high pressure under different oxygen fugacities

Electrical conductivities of pyroxenite were measured between frequencies of 10^?1 and 10⁶ Hz in a multi-anvil pressure apparatus using different solid buffers (Ni+NiO, Fe+Fe₃O₄, Fe+FeO and Mo+MoO₂) to stabilize the partial pressure of oxygen. The temperature ranged from 1073 to 1423 K (800 to 1200 °C) and the pressure from 1.0 to 4.0 GPa. We observe that: (1) the electrical conductivity (σ) of pyroxenite depends on frequency; (2) σ tends to increase with rising temperature (T), and Log σ and 1/T obey a linear Arrhenius relationship; (3) under control of the buffer Fe+Fe₃O₄, σ tends to decrease with rising pressure, nevertheless the activation enthalpy tends to increase. For the first time we have obtained values for the activation energy and activation bulk volume of the main charge carriers, which are (1.60±0.07) eV and (0.05±0.03) cm³/mol, respectively; (4) for a given pressure and temperature, σ tends to rise with increased oxygen fugacity, whereas the activation enthalpy and preexponential factor tend to decrease; and (5) the behaviour of the electrical conductivity at high temperature and high pressure can be reasonably interpreted by assuming that small polarons provide the dominant conduction mechanism in the pyroxenite samples.     

Effect of W co-doping on the optical,magnetic and electrical properties of Fe-doped BaSnO3

The effect of W co-doping on the optical, magnetic and electrical properties of Fe-doped BaSnO₃ has been studied. Polycrystalline BaSnO₃, BaSn_0.96Fe_0.04O₃ and BaSn_0.95Fe_0.04W_0.01O₃ samples were prepared using solid state reaction. In the analysis of powder X-ray diffraction patterns, the samples were found to be free of secondary phases. Diffuse reflectance spectra evidenced the substitution of Fe and W for Sn in the host BaSnO₃. Micro-Raman spectra confirmed the existence of oxygen vacancies in the samples. Upon W-1% co-doping, the ferromagnetic character of Fe-4% doped BaSnO₃ is suppressed drastically and its Curie temperature is reduced to 310 K from 462 K. The existence of F-centers and ferromagnetic interactions at room temperature is evidenced by the electron paramagnetic resonance and ferromagnetic resonance signals observed in the electron spin resonance spectra of the undoped and Fe-4% doped, (Fe-4% and W-1%) co-doped BaSnO₃ samples respectively. Suppression of ferromagnetism upon W co-doping is due to the fact that each W⁶⁺ ion donates two electrons to the host lattice and it reduces the number of oxygen vacancies that are essential for ferromagnetism to exist in the Fe-doped BaSnO₃ samples.     

Effect of Bi2O3 on EPR, optical transmission and DC conductivity of vanadyl doped alkali bismuth borate glasses

Glasses with composition xBi₂O₃·(30−x)M₂O·70B₂O₃ (M=Li, Na) containing 2 mol% V₂O₅ have been prepared over the range 0≤x≤15 (x is in mol%). The electron paramagnetic resonance spectra of VO²⁺ of these glasses have been recorded in the X-band (≈9.3 GHz) at room temperature (RT≈300 K). Spin Hamiltonian parameters, g_∥, g_⊥, A_∥, A_⊥, dipolar hyperfine coupling parameter, P, and Fermi contact interaction parameter, K, have been calculated. The molecular orbital coefficients, α² and γ², have been calculated by recording the optical transmission spectra. In xBi₂O₃·(30−x)Li₂O·70B₂O₃ glasses there is decrease in the tetragonality of the V⁴⁺O₆ complex for x up to 6 mol% whereas for x≥6 mol%, tetragonality increases. In xBi₂O₃·(30−x)Na₂O·70B₂O₃ glasses there is increase in the tetragonality of the V⁴⁺O₆ complex with increasing x. The 3d_xy orbit expands with increase in Bi₂O₃:M₂O ratio. Values of the theoretical optical basicity, Λ_th, have also been reported. The DC conductivity increases with increase in temperature. The order of conductivity is 10⁻⁵ ohm⁻¹ m⁻¹ at low temperature and 10⁻³ ohm⁻¹ m⁻¹ at high temperature. The DC conductivity decreases and the activation energy increases with increase in Bi₂O₃:M₂O ratio.     

碱土金属氧化物阳离子2MO+(M=Ca, Sr, Ba) 介入N2O与CO反应的理论研究

本文采用UB3LYP/6-311G(2d)+SDD//CCSD(T)/6-311+G(2d)+SDD方法, 计算研究了气相中碱土金属氧化物阳离子2MO+(M=Ca, Sr, Ba)参与N2O (X1∑+) + CO (X1∑+) → N2 (X1∑+g) + CO2 (X1∑+g) 的反应机理. 通过计算亲氧性得到在三种氧化物阳离子中只有2CaO+从N2O得到O原子并传递给CO的过程是热力学允许的. 碱土金属氧化物阳离子2MO+参与主题反应的机理通过以下两种方式进行, 其一为2MO+从N2O获取O原子生成2MO2+, 进而向CO提供O原子得到2MO+和CO2, 该过程为催化反应机理; 其二为2MO+先与N2O复合生成中间体IM1, 之后IM1继续与CO复合生成中间体IM2', 经过一系列反应过程最终生成2MO+, N2和CO2. 通过对两种反应过程的热力学性质和动力学因素分析得到, 2MO+(M=Ca, Sr, Ba)参与反应N2O (X1∑+) + CO (X1∑+) → N2 (X1∑+g) + CO2 (X1∑+g)的机理为后一路径, 所得结果与实验观测相符.     

碱土金属氧化物阳离子2MO+(M=Ca,Sr,Ba)参与N2O与CO反应理论研究

本文采用UB3LYP/6-311G(2d) +SDD//CCSD(T)/6-311+ G(2d) +SDD方法,计算研究了气相中碱土金属氧化物阳离子2MO+ (M=Ca,Sr,Ba)参与N2O (X1∑+)+CO(X1∑+)→N2(X1∑g+)+CO2 (X1∑g+)的反应机理.通过计算亲氧性得到在三种氧化物阳离子中只有2CaO+从N2O得到O原子并传递给CO的过程是热力学允许的.碱土金属氧化物阳离子2MO+参与主题反应的机理通过以下两种方式进行,其一为2 MO+从N2O获取O原子生成2MO+,进而向CO提供O原子得到2MO+和CO2,该过程为催化反应机理;其二为2MO+先与N2O复合生成中间体IM1,之后IM1继续与CO复合生成中间体IM2',经过一系列反应过程最终生成2MO+,N2和CO2.通过对两种反应过程的热力学性质和动力学因素分析得到,2 MO+ (M=Ca,Sr,Ba)参与反应N2O(X1∑+)+CO(X1∑+)→N2(X1∑g+)+CO2(X1∑g+)的机理为后一路径,所得结果与实验观测相符.     

AC conductivity behaviour and charge carrier concentrations of some vanadate glassy system

The investigation of wide range of temperature and frequency dependent conductivity of some semiconducting glassy system reveals DC conductivity, crossover frequency and frequency exponent. The composition dependence of AC conduction activation energy and the permissible energy of polaron migration have also been computed. The Nernst-Einstein relation proves that the concentration of mobile charge carriers does not undertake a substantial part in electrical conduction.     

Synthesis of P-type transparent conducting silver:indium oxide (AIO) thin films by reactive electron beam evaporation technique

Present paper reports the synthesis, electrical and optical properties of p-type conducting and transparent silver indium oxide (AIO) thin films prepared on glass substrates by reactive electron beam evaporation technique at three substrate temperatures (50, 200 and 250 °C) and at five evaporation rates (0.05 to 16.0 nm/s). The source material is pure powders of Ag₂O:In₂O₃=50:50 mol%. The AIO films are amorphous. The films, though not corresponding to Delafossite crystal structure, exhibit p-type conductivity, when prepared at an evaporation rate of 0.05 nm/s at all the three substrate temperatures. With increasing filament current, it is observed that (i) the electrical resistivity decreases and (ii) the refractive index of the films (at 632.8 nm, and is in the range: 1.219-1.211) decreases. The work function (effective Fermi level) has been measured on these samples by Kelvin Probe method. The results are explained on the basis of partial ionic charge and localization of covalent bonds in the AIO thin films.     

Surface science of diamond: Familiar and amazing

The crystal structure of diamond is identical with that of its more common semiconductor relatives silicon and germanium. Consequently, a number of surface properties in terms of reconstructions, surface states and surface band diagrams are similar as in the case of Si or Ge. But diamond also exhibits a number of unusual and potentially very useful surface properties. Particularly when the surface dangling bonds are saturated by monovalent hydrogen atoms (donor-like), surface states are removed from the gap, the electron affinity changes sign and becomes negative, and the material becomes susceptible to an unusual type of transfer doping where holes are injected by acceptors located at the surface instead of inside the host lattice. These surface acceptors can in the simplest case be adsorbed molecules conveniently chosen by their electron affinity, but they can also be solvated ions within atmospheric water layers or electrolytes in contact with the hydrogenated diamond surface. In this article the surface properties of diamond will be reviewed with special emphasis on this new kind of doping mechanism.