NO2 sensing properties of YSZ-based sensor using NiO and Cr-doped NiO sensing electrodes at high temperature

Nickel oxide and chromium-doped nickel oxide (Ni_0.95Cr_0.03O_1−δ ) were prepared by thermal decomposition of nitrates. The obtained NiO and Ni_0.95Cr_0.03O_1−δ samples were utilized as sensing electrodes (SEs) in yttria-stabilized zirconia (YSZ)-based sensors for detection of NO₂ at 800 °C under wet condition (5 vol.% H₂O). While the mixed-potential-type planar sensor attached with NiO-SE gave rather large NO₂ sensitivity, the sensor attached with Ni_0.95Cr_0.03O_1−δ -SE exhibited fast recovery rate with an acceptable sensitivity. The Δemf (electromotive force) of the sensors varied linearly with NO₂ concentration in the examined range of 50–400 ppm on a logarithmic scale. Based on the results of measurements for polarization, complex impedance and gas phase catalysis, the fast recovery was attributable to the high rate for the anodic reaction of O₂ at the Ni_0.95Cr_0.03O_1−δ /YSZ interface, and the lower NO₂ sensitivity was caused by both the high rate for the anodic reaction of O₂ and the high degree for the gas phase conversion of NO₂ to NO.     

Mixed-potential-type zirconia-based NOx sensor using Rh-loaded NiO sensing electrode operating at high temperatures

The improvement in sensing characteristics of mixed-potential-type NO₂ sensor based on an yttria-stabilized zirconia (YSZ) plate was examined by an addition of noble metal to NiO sensing-electrode. Among the various noble metals (Pt, Rh, Ir, Pd and Ru) examined, Rh was found to give a significant enhancement in NO₂ sensitivity. In addition, this enhancement was maximum when the Rh content in NiO-SE was 3 wt.%. The sensitivity (emf) to 50 ppm NO₂ was as high as about 77 mV for the sensor using the 3 wt.% Rh-loaded NiO-SE at 800 °C under the wet condition (5 vol.% H₂O). The NO₂ sensitivity was hardly affected by the change of H₂O and CO₂ concentration in the examined range of 5–15 and 5–20 vol.%, respectively, and was almost stable for about 50 days tested at 800 °C. It was speculated that the improved kinetic effect of Rh loading on the cathodic reaction of NO₂ at the interface of SE/YSZ was the major contributing factor for the enhanced NO₂ sensitivity of the sensor.     

High-temperature NO or NO2 sensor using stabilized zirconia and tungsten oxide electrode

Stabilized zirconia-based electrochemical devices for which the sensing electrode was provided with a single-metal oxide were tested for NO and NO₂ sensing properties at high temperature. Among the many single-metal oxides examined, WO₃ was found to give the best sensing properties to NO and NO₂ at 500–700°C. The EMF response of the WO₃-attached device was linear to the logarithm of NO or NO₂ concentration. The response and recovery kinetics were speedy. The device gave very small cross-sensitivities to H₂, CO, CH₄, CO₂ and water vapor. The sensing mechanism involving mixed-potential was confirmed from the measurements of polarization curves.     

Temperature dependence of the sensitivity of a long-range surface plasmon optical sensor

The temperature dependence of the sensitivity of an optical sensor based on long-range surface plasmon resonance (LRSPR) is studied via theoretical modeling. Both the ‘angular interrogation’ and the ‘wavelength interrogation’ modes of operation are studied. In addition, the variation of the full width at half maximum of the LRSPR ‘reflectance dip’ is also studied as a function of temperature, which ultimately determines the temperature dependence of the sensitivity of the sensor when the reflectance is monitored at a fixed incident angle (‘reflectance interrogation’). It is found that while most of the time only the ‘reflectance interrogation’ mode leads to improved sensitivity for the LRSPR sensor compared to a conventional SPR sensor, the temperature stability of the operation of the LRSPR sensor is generally higher than (or at least comparable to) that of the SPR sensor. PACS 73.20.Mf; 07.07.Df     

Investigation of the electrode effects in mixed potential type ammonia exhaust gas sensors

Mixed potential ammonia exhaust gas sensors provide a high capability for applications in harsh environments when appropriate means are conducted to stabilize the electrodes catalytic activity. The discussed sensor utilizes oxygen ion conducting yttria stabilized zirconia and gold electrodes, one of which is covered with an SCR active film to establish ammonia sensitivity and selectivity. The used SCR catalyst is well-known and developed especially for ammonia SCR exhaust gas aftertreatment systems. Electrochemical half-cell measurements vs. a Pt reference indicate that both electrode configurations are electro catalytically active for ammonia oxidation, but the activity is more pronounced at the additional SCR catalyst layer. The results of the half-cell tests including ammonia dependent voltage and oxygen interference agree very well with the performance of the ammonia sensor device. The behavior of the catalyst electrode cover is characterized separately by activity measurements of powders. The sensing mechanism combines electrochemical reactions at the three phase boundary and chemical reactions at the catalyst material.     

Temperature dependence of ferromagnetic resonance in permalloy/NiO exchange-biased films

The temperature dependencies of the ferromagnetic resonance (FMR) linewidth and the resonance field-shift have been investigated for NiO/NiFe exchange-biased bilayers from 78 K to 450 K. A broad maximum in the linewidth of 500 Oe, solely due to the exchange-bias, is observed at ≈150 K when the magnetic field is applied along the film plane. When the magnetic field is applied perpendicular to the film plane, the maximum in the linewidth is less pronounced and amounts to 100 Oe at the same temperature. Such a behavior of the FMR linewidth is accompanied with a monotonic increase in the negative resonance field-shift with decreasing temperature. Our results are compared with the previous experimental FMR and Brillouin light scattering data for various ferromagnetic/antiferromagnetic (FM/AF) structures, and suggest that spin dynamics (spin-wave damping and anomalous resonance field-shift) in the FM/AF structures can be described in a consistent way by a single mechanism of the so-called slow-relaxation.     

Temperature dependence of electron magnetic resonance and magnetization in NiO nanorods

For NiO nanorods of 5 nm diameter prepared by sol-gel technique, variations of the magnetization M with temperature T (5-370 K) and magnetic field H up to 55 kOe are reported. Also, temperature variations of the EMR (electron magnetic resonance) parameters (intensity I₀, linewidth ΔH and resonance field H_r) of an observed line due to uncompensated spins are followed for The M vs. H and T variations yield a blocking above which the data fits modified Langevin function with magnetic moment μ_p?1240 μ_B/particle. For the EMR line, I₀ decreases rapidly for T<T_B, and the line broadens and shifts to lower H with lowering T, following the lineshift δH_r=(ΔH)ⁿ with n?2.8. This is close to the value of n=3 expected for randomly oriented particles.     

Polarization dependence in the UV laser desorption of NO from NiO(100)

- and -polarized radiation. When the yield is related to the incident photon flux, desorption cross sections of (1.9±0.3)×10^-17 cm² and (3.3±0.5)×10^-17 cm² for - and -polarized light, respectively, are deduced. In order to assess the importance of substrate excitation the optical constants of NiO have been determined for the photon energy employed. When the desorption yield is then related to the photon flux absorbed in the NiO film, much larger cross sections are obtained, and an even larger effectiveness of -polarized light. For a direct optical excitation of charge transfer states the implications for the symmetry character of the states involved are discussed. It is concluded that excitations to A^′′ states are preferred. Received: 21 October 1998     

InSb霍尔传感器输出电压温度特性的研究

对InSb霍尔元件在－135～65℃内的霍尔电压的温度特性进行了测量,研究在恒流源和恒压源条件下其输出电压随温度的变化情况,并对其工作温度、线性范围及应用进行了探讨。     

Potentiometric DO detection in water by ceramic sensor based on sub-micron RuO2 sensing electrode

An alumina sensor using sub-micron RuO₂ sensing electrode (SE) was fabricated and examined for potentiometric dissolved oxygen (DO) detection in water at a temperature range of 9–35 °C. The electromotive force (emf) response at these temperatures was linear to the logarithm of DO concentration in the range from 0.6 to 8.0 ppm (log[O₂], −4.71 to −3.59). RuO₂-SE displays a Nernstian slope of −41 mV per decade at pH 8.0. It was also found that the response/recovery time to DO changes were sluggish as the water temperature cools down. Response time T ₉₀ to DO changes increased from 8 min at a temperature of 23 °C to about 30 min at a temperature of 9 °C. The proton conductivity of hydrous RuO₂ appears to be due to the dissociative adsorption of water and the formation of acidic OH groups in Ru (III,IV) cluster ions. In strong alkaline solutions, the sensor’s emf exhibited a mixed potential of fast and slow electrochemical reactions involving DO, RuO₄ ²⁻ and OH⁻ ions. The results also revealed that as pH of the solution increases to pH 10.0–13.0, the response/recovery rate becomes faster, stabilizing more or less quickly depending upon the solution alkalinity. Scanning electron microscopy, energy dispersive X-ray-analysis and impedance spectroscopy techniques were used to examine respectively the morphology, crystalline structure and electrochemical behaviour of sub-micron RuO₂ oxides.     

Temperature dependence of the low energy auger spectrum of NiO(100)

The temperature dependence of the Auger electron spectrum of NiO(100) has been observed in order to assign 10 features found below 300 eV. Six features are attributed to diffraction of true secondary electrons generated within the crystal. The others are due to substrate or surface impurity Auger peaks. The difficulties of identifying impurities and diffraction features are emphasised.     

Dependence of NO2 sensitivity on thickness of oxide-sensing electrodes for mixed-potential-type sensor using stabilized zirconia

The effect of thickness of oxide-sensing electrode (SE) on NO₂ sensitivity of the planar sensor based on yttria-stabilized zirconia (YSZ) was examined at high temperatures. The sensitivity of the sensor increased with decreasing thickness of SE, and the highest sensitivity was obtained by using the thinnest layer of Cr₂O₃–SE (2.7 μm) at 700 °C. In the case of NiO–SE, the highest sensitivity was observed for the sensor using the 4-μm-thick SE even at a high temperature of 850 °C. Based on the results of the measurements for the complex impedances, the polarization curves, and the gas-phase NO₂ decomposition catalysis, it was confirmed that the catalytic activity to the gas-phase NO₂ decomposition on the oxide–SE matrix played an important role in determining the NO₂ sensitivity of the present sensors.     

In situ FTIR investigation of adsorption properties of sub-micron Cu2O-doped RuO2 sensing electrode of planar potentiometric pH sensor

In situ Fourier transform infrared spectroscopy (FTIR) was used to study adsorption properties of 20?mol% Cu₂O-doped RuO₂ sensing electrode (SE) screen-printed on the platinised alumina substrate of the planar electrochemical pH sensor and subsequently sintered at 800?°C. Morphology and properties of developed SEs were characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy and FTIR techniques. It was shown that both Cu₂O doping and changes in the sintering condition of the SE affected morphology and adsorption spectra of 20?mol% Cu₂O-doped RuO₂. Fundamental vibration frequencies of ruthenium?Coxygen bond at a temperature of 23?°C as well as region above fundamental frequencies for the sub-micron 20?mol% Cu₂O-doped RuO₂-SE were identified.     

An all-solid-state potentiometric SO2 gas sensor with solid reference electrode

A SO₂ sensor based on Na-β-Al₂O₃ interfaced with an auxiliary electrode of Na₂SO₄ formed in-situ and a solid mixture of Fe₃O₄, Fe₂O₃, 3Na₂O·5Fe₂O₃ as the reference electrode was developed. The sensor displayed a good response to changes in the partial pressure of SO₂ with a linear relationship between the measured emf and the logarithmic values of the partial pressure of SO₂, as predicted by the Nernstian equation. Using an electron probe X-ray microanalyser, the formation of a Na₂SO₄ reaction layer was confirmed on the surface of Na-β-Al₂O₃ tube due to surface reaction with the SO₂ gas.     

Temperature dependence of energy dissipation in type I superconductors

Energy dissipation due to the movement of the magnetic flux in superconducting tin was studied by means of the torsion pendulum technique. The study was made as a function of the mean velocity of vortices, applied magnetic field and temperature. A phenomenological expression for the energy dissipation is proposed. This model explained our experimental results as well as these obtained previously by Houston and Smith.     

Temperature dependence of the magnetization in the mixed state of superconducting alloys

The theory of Abrikosov of the immediate subcritical region in the mixed state is extended by means of the generalized Ginzburg-Landau theory to temperatures belowT _c and arbitrary mean free pathl of the electrons. The results for the magnetization and the free energy can still be presented in the form derived by Abrikosov apart from the fact thatκ is replaced by a new parameterκ ₂(T). The slope of the curveκ ₂/κ versust=T/T _c att=1 is found to decrease monotonically from ?0.105 to — (1.367-0.136κ ^?2) asl increases from zero to infinity. The results for short mean free paths are consistent with experiment, in particular,κ ₂ is always larger thanκ in the vicinity ofT _c . But the experimental temperature dependence ofκ ₂/κ in pure Nb is much higher than the theoretical one.     

Potentiometric carbon dioxide sensor based on thin Li3PO4 electrolyte and Li2CO3 sensing electrode

Potentiometric CO₂ gas sensors with thin-film lithium phosphate (Li₃PO₄) electrolytes were developed by using radio frequency (RF) magnetron sputtering. Li₂CO₃ and a mixture of Li₂TiO₃ and TiO₂ were used as sensing and reference electrodes, respectively. By using the RF sputtering deposition process, we obtained a dense, crystalline, thin-film Li₃PO₄ electrolyte with good adhesion on the Al₂O₃ substrate. The thin-film Li₃PO₄ electrolyte had good ionic conductivity, i.e., 2.15?×?10^?6 S cm^?1 at 500 °C, and its activation energy was 0.97 eV. The thin-film Li₃PO₄ electrolyte was suitable for the miniaturization of potentiometric CO₂ sensors. The thin-film potentiometric CO₂ sensor provided relatively good sensing response for overall CO₂ concentrations (500 to 3,000 ppm and 5 to 20 %) at 500 °C. The Nernstian slope of 78.2 mV/decade obtained for CO₂ concentrations from 5 to 20 % at 500 °C was close to the theoretical value (76.6 mV/decade). Although the sensor’s reading deviated from the theoretical value at low CO₂ concentrations (500 to 3,000 ppm), the sensor provided better sensing performance than a potentiometric CO₂ sensor with a thick electrolyte. As a result, it was assumed that the thin-film sensor could be used to monitor the overall concentration of CO₂ in the environment.