Characteristics of thick-film CO2 sensors based on NASICON with Na2CO3-CaCO3 auxiliary phases

Potentiometric CO₂ sensors were fabricated using a NASICON (Na_1+x Zr₂Si_xP_3−x O₁₂) thick film and auxiliary layers. The powder of a precursor of NASICON with high purity was synthesized using the sol-gel method. Using the NASICON paste, an electrolyte was prepared on the alumina substrate through screen printing and then sintered at 1000^∘C for 4 h. In the present study, as new auxiliary phases, a series of Na₂CO₃-CaCO₃ system was deposited on the Pt sensing electrode. The electromotive force (EMF) values were found to be linearly dependent on the logarithm of the CO₂ concentration in the range of 1000–10000 ppm. The device to which Na₂CO₃-CaCO₃ (1:2) was attached showed good sensing properties at low temperatures.     

Potentiometric Gas Sensors for Oxidic Gases

Solid electrolyte-based electrochemical devices combined with an auxiliary phase of oxyacid salt have, in this decade, emerged as new attractive sensors to detect oxidic gases of CO₂, NO, NO₂ and SO₂. Various combinations of solid electrolytes and auxiliary phases as well as various new single or multi-component auxiliary phases have been exploited to improve the gas sensing properties and stability of these devices. Some of the potentiometric sensors developed e.g., CO₂ sensors using NASICON and Li₂CO₃-CaCO₃, NO₂ sensors using NASICON and NaNO₂-Li₂CO₃ and SO₂ sensors using MgO-stabilized zirconia and Li₂SO₄-CaSO₄-SiO₂, exhibit excellent gas sensing performances in laboratory tests and appear to be promising for monitoring the respective gases in ambient environments and/or combustion exhausts. This paper aims at describing our exploratory works on and the state of the art of these potentiometric gas-sensing devices.     

Capacitive Type Gas Sensors

Current status of capacitive type gas sensor were reviewed in this paper. Although the number of publications on capacitive type sensors has been limited so far, capacitive type sensors have good prospects given that the capacitor structure is so simple enabling miniaturization and achieving high reliability and low cost. Among the reported capacitive type sensors, detection of gas based on a change in dielectric layer thickness is most promising. On this point of view, capacitive type CO₂ and NO sensors using depletion layer formed at p-n junction of oxide semiconductor were introduced in detail. In addition, commercial capacitive type sensors for monitoring CO₂ based on this principle were mentioned. CO₂ concentration in office can be successfully monitored by the developed capacitive type CO₂ sensor.     

Electrochemical Sensors for CO/NOx Detection in Automotive Applications

Recent progress in the development of a -alumina gas sensor for automotive applications is reported. The sensing device consists of two solid electrolytes (namely a thin film of sodium sulfate deposited on -alumina by appropriate treatment in a gaseous atmosphere), with two electrodes having different catalytic properties, one made of platinum, the other of gold. The -alumina component was prepared as sintered pellets by pressing and as thick films by screen-printing. The electrical response of these materials at different temperatures in the range 300° to 800°C and under various gases (CO, NO, NO_x) with dilution in pure air in the range 5 ppm to 5 vol% was investigated and studied as a function of the preparation technique. The dense ceramic and the thick film designs behave similarly. A sensor prototype based on the thick film design was then developed and tested. All the experimental results prove that the sensor can be successfully used for selective detection of CO and NO_x. The selectivity results from an appropriate choice of the working temperature of the sensing element. At low temperatures (300 to 400°C) NO₂ can be selectively detected in the presence of CO; the opposite happens in the higher temperature range (550 to 650°C).     

On the Relationship Between the Grain Size and Gas-Sensitivity of Chemo-Resistive Metal-Oxide Gas Sensors with Nanosized Grains

In this work we elaborate the effect of grain size on the sensitivity of chemo-resistive metal-oxide gas sensors with nanosized grains. The effective carrier concentration in nanocrystalline SnO₂ sensors with various grain sizes is calculated as a function of the surface state density. This involves numerical computation of the charge balance equation (i.e., the electroneutrality condition) using approximated analytical solutions of Poissons equation for small spherical crystallites. The calculations demonstrate a sharp decrease in the carrier concentration when the surface state density reaches a critical value that corresponds to a condition of fully depleted grains, namely when nearly all the electrons are trapped at the surface. Assuming that the variations in the surface state density are induced by surface interactions with the gas phase, these calculations enable to simulate the response curves of nanocrystalline SnO₂ gas sensors. The simulations show that the conductivity increases linearly with decreasing trapped charge densities, and that the sensitivity to the gas-induced variations in the trapped charge density is proportional to 1/D, where D is the average grain size.     

Influences of Fe Element on the Structural and Electrochemical Performances of LiNi0.5Co0.2Mn0.3O2 Cathode Materials

The effect of Fe element on the structural and electrochemical performance of the Layered LiNi_0.5Co_0.2Mn_0.3O₂ materials with various Fe-doped amounts synthesized by high-temperature solid state method had been studied quantitatively and in detail. The structural and morphological of the prepared samples were characterized by X-ray diffraction patterns (XRD) and scanning electron microscopy (SEM). The study results show that the discharge capacity and cycling performance of the LiNi_0.5Co_0.2Mn_0.3O₂ all reduced by Fe doping, that is mainly attributed to the aggravated disorder degree of the layered structure and charge transfer resistance. Fe content should be controlled strictly in the layered LiNi_1?x?yCo_xMn_yO₂ cathode materials production process.     

Glycolate tantalum based solutions for the sol-gel spin-coating deposition of SrBi2Ta2O9 thin films

Abstract

The reaction of tantalum ethoxide with a glycol solvent produces the interchange of the ethoxide groups with the glycol. As a result, a polymeric derivative is formed with a high resistance towards hydrolysis. Compounds of Sr(II) and Bi(II) can be added to this Ta-glycol sol, leading to strontium bismuth tantalate (SBT) precursor solutions stable in air. These solutions were spin-coated onto two substrates: Pt/TiO₂/SiO₂/(100)Si and Ti/Pt/Ti/SiO₂/(100)Si. Crystallisation of the SBT phase was carried out by a first formation of a fluorite phase that evolves to the layered perovskite at temperatures over 600°C. During crystallisation, a larger tendency to the formation of a substrate/film interface was observed in the films deposited onto Ti/Pt/Ti/SiO₂/(100)Si than onto Pt/TiO₂/SiO₂/(100)Si. A remanent polarisation of P_r5 μC/cm² and a coercive field of E_c <100 kV/cm were measured in the films on Pt/TiO₂/SiO₂/(100)Si. These films retain its remanent polarisation, P_r, up to 10⁵seconds and are fatigue-free up to 10⁹ cycles.     

Effects of Magnetic Field on Synthesis and Thermoelectric Properties of NaCoO2

We synthesized polycrystalline sodium cobalt oxide (NaCoO₂) by using solid state reaction (SSR) method in a magnetic field. The powder of Na₂CO₃ and Co₃O₄ were mixed by ball milling and compacted in a magnetic field. The characterization of microstructure of powder size and crystal structure were analyzed through XRD. Thermoelectric properties and the lattice parameter of NaCoO₂ showed little change in magnetic field. The lattice parameters of NaCoO2 are a = 2.8443 Å, b = 2.8443 Å, and c = 10.8091 Å in the hexagonal structure (a = b ≠ c).     

Synthesis and Characterization of Bi-Fe-O Amorphous Nanoparticles for Photocatalysis by Sol-Gel Method

Abstract

Bi-Fe-O amorphous nanoparticles were synthesized via a facile sol-gel method using tartaric acid as the chelating agent. The samples were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and UV-vis. Photocatalysis of Bi-Fe-O amorphous nanoparticles was further examined by monitoring the degradation of Rhodamine B dye in an aqueous solution under visible light irradiation with H₂O₂. It was proved that Bi-Fe-O amorphous nanoparticles showed higher degradation rate under visible-light irradiation with H₂O₂ than without H₂O₂.     

Crystallization of Zr Based Oxide with Glass Forming Additives for Gate Dielectric Applications

In this study, Si, Al, and Bi have been investigated as a glass forming additive. Addition of glass forming materials is effective on stabilization of amorphous phase for Zr based films. The higher crystallization temperature results from the more additives. Addition of heavier atom is more effective on enhancing dielectric constant but results in lowering crystallization temperature. Addition of Si results in the most stable amorphous with significant reduction of dielectric constant. When the atomic ratio of Si over (Si + Zr) of about 0.55 is annealed at 950°C for 1 min, any crystallization behaviors are not noticed with dielectric constant of 12. On the other hand, addition of Al causes moderate improvement of crystallization behavior with small sacrifice of dielectric constant. The amorphous films of Zr_{1 ? x} Al _x O _y (X = 0.55) remain amorphous up to 800°C anneals with dielectric constant of 15.     

Influence of Defect Orientation on Electrical Insulating Properties of Plasma-Sprayed Alumina Coatings

The influence of the microstructure (pores and cracks) on electric properties of plasma-sprayed alumina coatings was investigated using the so-called Scanning Electron Microscope Mirror Effect (SEMME) technique.Coatings were sprayed with different alumina feedstock powders on various atmospheres using a CAPS (‘Controlled Atmosphere Plasma Spraying’). Microstructures with various amount of porosity and cracks orientation distributions were analysed. Both outer surfaces and cross-sections of alumina coatings have been analysed by SEMME technique using two complementary modes (measurement of absorbed current and mirror methods). Originally developed to study the behaviour of injected electrons and related phenomena, such as trapping ability, detrapping process and relaxation phenomena in bulk insulating materials, the SEMME technique was successfully applied, in this study, to porous coatings. It is proved that cracks orientation modifies both motion and trapping of charges and therefore the dielectric properties of plasma-sprayed alumina coatings.     

Fabrication and characteristics of piezoelectric PZT cantilever for high speed atomic force microscopy

Abstract

A PZT actuator integrated onto cantilever structure was fabricated for high speed atomic force microscopy (AFM). Five different electrodes were used to investigate the effect of top electrodes on the adhesion and the electrical properties in the PZT capacitors. The PZT capacitors with RuO₂ top electrodes exhibited the best characteristics of five electrodes. The tip deflection and the resonant frequency of the PZT actuator were 11 μim at 10 V and 79 kHz, respectively. The PZT actuator provided much better AFM image quality and imaging speed than those done by using the conventional bulk PZT tube scanner. The creep distortion in the AFM image was greatly improved by using the high speed PZT film actuator.     

Sol-gel Synthesis and Photoluminescence Characterization of Ba2SiO4:Eu2+ Green Phosphors for White-LED Application

In this paper, Ba₂SiO₄:Eu²⁺ green phosphor was synthesized by sol-gel method. TGA-DTA, XRD, SEM and PL spectra were used to characterize the as-prepared phosphors. The phosphors are composed of nanoparticles with 60 nm grain size and exhibit green light with a broad peak around 500 nm. The relationship between crystal growth, morphology and luminescent properties was studied. The structure and luminescence properties of phosphors synthesized in different conditions were also discussed.     

Preparation of MoP2 nanoparticles as a novel anode material for sodium ion batteries

ABSTRACT

We identify the most important factor affecting the delay precision detonators by orthogonal experiments, thus optimize formulations to expect to get a better precision detonator recipe. Ultrafine ms delay due to the small particle size drug, the distance between the particles is small, a small gap, in the natural body of air the air is delayed relatively small, although the moisture absorption, but the overall water was reduced, and therefore can effectively avoid vibration combustion and second volume drift, therefore burning more stable, so the delay time stability, high delay precision, good storage performance.     

Chemical processing and properties of Sr2(Ta,Nb)2O7 thin films

Abstract

The crystallographic orientation, microstructure and electrical properties of Sr₂(Ta, Nb)₂O₇ thin films strongly depended on the composition (Ta:Nb). Post-annealing at 850°C was effective for the improvement of some properties. The thin films with relatively Nb-rich compositions, such as Sr₂(Ta_0.6Nb_0.4)₂O₇ and Sr₂(Ta_0.5Nb_0.5)₂O₇, showed the (0k0) preferred orientation. The Sr₂(Ta_0.5Nb_0.5)₂O₇ thin film had a lamination layer structure after the post-annealing at 850°C for 6 min in oxygen. The characteristic microstructure originated in the crystallographic orientation of (0k0), which is the cleavage plane, and influenced electrical properties. The dielectric constant little change with the composition, however, the P-E hysteresis properties improved with the Nb content.     

Structural and Dielectric Characterization of Sol-Gel Fabricated PbTiO3 Thin Films Doped with Lanthanide Ions

Lanthanide elements doped PbTiO₃ thin films were prepared by a modified sol-gel method via spin-coating on platinized silicon substrates. The films microstructure and phase composition were investigated by means of scanning electron microscopy, X-ray diffractometry and Raman spectroscopy. Small signal dielectric properties of the films were characterized at different temperatures and doping element concentration. It is shown that dielectric constant, loss tangent and Curie transition temperature of lanthanide elements doped thin films correlate with concentration and ionic radii of these elements. The results obtained are discussed from the point of view of substitution type and compared to some extent to the data, reported by other research groups.     

Photoluminescence properties of Y2O3co-doped with Eu and Bi compounds as red-emitting phosphor for white LED

Bismuth doped Y₂O₃: Eu was used as a red phosphor with a very high efficiency and an appropriate emission wavelength of around 310–400 nm. This red phosphor was synthesized by the solid state reaction which is normally used in the field of white LEDs. In this study, we synthesized Y₂O₃: Eu, Bi phosphors using a solid state reaction. We investigated the effect of the Eu^{3 +} and Bi^{3 +} concentrations and additive fluxes on the emission characteristics. The fabricated phosphors were investigated by analyzing their particle size and crystal structure with scanning electron microscopy and X-ray diffraction (XRD). Their photoluminescence (PL) spectra were also measured at room temperature.     

Fabrication of a Lithium Sensor Based on LiYO2 by Liquid Phase Processing

A galvanic cell was constructed to measure the activity of lithium in liquid alloys. LiYO₂ solid electrolyte tubes were made by slip casting. Y₂O₃-12.5% MgO was selected as the lid composition due to its inertness to molten lithium and optimum strength. The tube and lid were joined by reaction bonding in which Li₂CO₃ acts as the bonding agent and also plays an important role as sintering additive. The tube-lid assembly was used in a galvanic cell to measure the emf of Li in Li-Sn and Li-Zn alloys at temperatures of 240–720°C. The emf results demonstrated the reproducible functioning of the sensor.     

Semi-Conductors with Mobile Ions Show a New Type of I-V Relations

Semi-conductors with mobile acceptors or donors show a new type of I-V relations. This paper presents experimental results for solid state devices based on copper oxide, found to be Cu₂O, which exhibit these I-V relations. The cells examined are Cu| Cu₂O| In and Cu| Cu₂O| Ag and similar ones tested at room temperature. The measured I-V relations are different from those reported for the same type of cells in the past, which were explained to be fixed by a Schottky barrier Cu| Cu₂O. We find that the I-V relations relax over a long time which we claim is due to ion redistribution. The new I-V relations can then be explained by assuming that Cu₂O is a mixed-ionic-electronic-conductor and adopting a theory developed by us in the past and modified to be applicable to the relevant defect model here. In this case the contribution of Schottky barriers is insignificant.     

Effects of functional electrical stimulation in denervated thigh muscles of paraplegic patients mapped with T 2 imaging

OBJECT: Functional electrical stimulation (FES) for paraplegic patients, with the long-term goal of ultimately restoring muscle function, is associated with several positive effects: improvement of blood circulation, skin condition, peripheral trophism and metabolism, prophylaxis against decubitus ulcer and better physical fitness. Since fibres of denervated muscles (lacking a supplying nerve) need to be activated directly, the fraction of elicited muscle tissue follows the geometric distribution of the electrical field, which can be simulated using electrophysiological computer models. Experimental validation of these results, however, has not yet been established. MATERIALS AND METHODS: We acquired T (2) parameter images using a multislice multi-spin-echo MR sequence before and immediately after FES in nine denervated paraplegic patients and three healthy subjects in order to visualise the geometric distribution of activation by electrically induced muscle stimulation in denervated versus innervated (healthy) thigh muscle. RESULTS AND CONCLUSION: After realigning and normalisation, maps of relative T (2) increase were calculated. The results demonstrate that the spatial distribution of short-term effects of FES of denervated muscle tissue of paraplegic patients who regularly perform FES can be visualised by T (2) parameter images. This may be used to refine models of the electrical field of FES in muscle and fibre activation in the future.