The electrical and thermal properties of sodium sulfate mixed with lanthanum sulfate and aluminum oxide

Sodium sulfate mixed with lanthanum sulfate and aluminum oxide was prepared and its phases and electrical properties were investigated. The Na₂SO₄−La₂ (SO₄)₃−Al₂O₃ sample maintains a Na₂SO₄-I-similar phase and exhibits higher electrical conductivity compared with unmixed sodium sulfate. Electromotive force (EMF) measurements were carried out by constructing the sulfur oxides concentration cell. The measured EMF was in good agreement with the calculated EMF, in the inlet SO₂ gas concentration from 100 ppm to 1%.     

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.     

Characteristics of the Na/beta-alumina/Na cell as a sodium vapor pressure sensor

The EMF and voltage-current characteristics for a galvanic cell with the configuration Na vapor (P₁)/sodium beta-alumina/Na vapor (P₂) were studied. It was verified that the EMF followed the Nernst relation over a wide pressure range. For example, when P₁ = 2 × 10^-2 mm Hg and beta-alumina temperature = 340°C, the measured EMF agreed with the calculated value in P₂ range from 10^-5 to 10^-2 mm Hg. At lower pressure range, the measured EMF showed a negative deviation. Coexisting argon gas did not influence the cell EMF characteristic. In an atmosphere containing oxygen, the measured EMF was very high at first. Then it decreased and finally approached a value which agreed with the Nernst equation after several hours. At low beta-alumina temperatures, current saturation was observed in the voltage versus current relation with the anode on the P₂ side. Although the sodium pressure could be determined from saturating current measurement, the measurable pressure range was narrower than that for EMF measurement. At high beta-alumina temperature, current saturation was not clear. Values of 6 × 10^-6 (Ω cm)^-1 for the electron conductivity and 6 × 10^-10 (Ω cm)^-1 for the hole conductivity at 340° were obtained for beta-alumina from the voltage-current characteristics at low sodium pressure.     

Characterization of iron oxide layers using Auger electron spectroscopy

Metals can form several kinds of oxides. Iron forms wustite (FeO), magnetite (FeO + Fe₂O₃ or Fe₃O₄) and haematite (Fe₂O₃). Iron oxides, especially magnetite, are used for insulation between the lamellas of an electromotor made of electromagnetic sheet. In this work, iron oxide layers were characterized on industrial samples of electromagnetic sheet by AES depth profile analysis, and iron oxides with known chemical composition were used as reference samples, i.e. a magnetite mineral and a standard haematite reference sample. The magnetite mineral was chosen because it can be found in nature in a very pure form. The selection of reference samples was also verified on samples with an oxide layer of known composition, which were prepared by sputter deposition. The composition of the sputtered oxide layers was analysed by the weight-gain method and Rutherford backscattering without the use of standard reference materials (SRM), and the results were then compared with those obtained by AES depth profile analysis.     

Stable and high conductivity ceria/bismuth oxide bilayer electrolytes for lower temperature solid oxide fuel cells

A highly conductive bismuth oxide/ceria bilayer electrolyte was developed to reduce solid oxide fuel cell (SOFC) operating temperatures. Bilayer electrolytes were fabricated by depositing a layer of Er_0.2Bi_0.8O_1.5 (ESB) of varying thickness via pulsed laser deposition and dip-coating on a Sm_0.2Ce_0.8O_1.9 (SDC) substrate. The open-circuit potential (OCP) and ionic transference number (t _i) of ESB/SDC electrolytes were tested in a fuel cell arrangement as a function of relative thickness, temperature, and with H₂/H₂O and CO/CO₂ on the anode side and air on the cathode side. These EMF measurements showed a significant increase in OCP and t _i with the bilayer structure, as compared to the cells with a single SDC electrolyte layer. Furthermore, improvement in the OCP and t _i of bilayer SOFCs was observed with increasing relative thickness of the ESB layers. Hence, the bilayer structure overcomes the limited thermodynamic stability of bismuth oxides and prevents electronic conductivity of ceria-based oxides in reducing atmosphere.     

Synthesis of manganese oxide nanocrystal by ultrasonic bath: effect of external magnetic field

A novel technique was used for the synthesis of manganese oxide nanocrystal by applying an external magnetic field (EMF) on the precursor solution before sonication with ultrasonic bath. The results were compared in the presence and absence of EMF. Manganese acetate solution as precursor was circulated by a pump at constant speed (7 rpm, equal to flow rate of 51.5 mL/min) in an EMF with intensity of 0.38 T in two exposure times (t_MF, 2 h and 24 h). Then, the magnetized solution was irradiated indirectly by ultrasonic bath in basic and neutral media. One experiment was designed for the effect of oxygen atmosphere in the case of magnetic treated solution in neutral medium. The as prepared samples were characterized with X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (HRTEM, TEM), energy-dispersive spectrum (EDS), and superconducting quantum interference device (SQUID) analysis. In neutral medium, the sonication of magnetized solution (t_MF, 24 h) led mainly to a mixture of Mn₃O₄ (hausmannite) and γ-MnOOH (manganite) and sonication of unmagnetized solution led to a pure Mn₃O₄. In point of particle size, the larger and smaller size of nanoparticles was obtained with and without magnetic treatment, respectively. In addition, the EMF was retarded the nucleation process, accelerated the growth of the crystal, and increased the amount of rod-like structure especially in oxygen atmosphere. In basic medium, a difference was observed on the composition of the products between magnetic treated and untreated solution. For these samples, the magnetic measurements as a function of temperature were exhibited a reduction in ferrimagnetic temperature to T_c = 39 K, and 40 K with and without magnetic treatment, respectively. The ferrimagnetic temperature was reported for the bulk at T_c = 43 K. A superparamagnetic behavior was observed at room temperature without any saturation magnetization and hysteresis in the measured field strength. The effect of EMF on the sample prepared in the basic medium was negligible but, in the case of neutral medium, the EMF affected the slope of the magnetization curves. The magnetization at room temperature was higher for the samples obtained in neutral medium without magnetic treatment. In addition, a horizontal shift loop was observed in neutral medium at low temperature.     

Influence of ceramic oxide materials on lithium based potentiometric CO2 sensors

In these potentiometric sensors, a mixed binary carbonate sensing material consisting of 90 mol% Li₂CO₃ and 10 mol% BaCO₃ was modified by adding ceramic oxide materials such as SiO₂, B₂O₃, La₂O₃, Bi₂O₃, CeO₂ and In₂O₃ in different mol% concentrations. Various sensors mixed with these external oxides have shown good performance at operating temperatures below 300 °C. Scanning electron microscopy reveals that a glassy sensing phase is formed in the sensing bi-carbonate by the addition of ceramic oxides and sintered at 600 °C for 1 h. The sensor mixed with SiO₂:B₂O₃:Bi₂O₃ in 1:2:1 mol% showed an excellent response and recovery characteristics and followed a fair Nernstian behavior with a ΔEMF/dec value of −48.18 at as low as 150 °C. The decrease in operating temperature is attributed to the enhanced lithium ion migration through the glassy sensing phase of the sensing electrode.     

Manipulating electromagnetic wave with the magnetic surface plasmon based metamaterials

In this work, we have investigated the optical properties of the magnetic metamaterials (MMs) consisting of periodically/randomly arranged ferrite rods. By calculating the photonic band diagrams and transmittance, we have identified a photonic band gap originating from the magnetic surface plasmon (MSP) resonance. In addition, by tuning the external magnetic field (EMF), an MM slab can be used as an optical switch. Our simulated results also suggest that the optical properties of the MMs are robust against the position disorder and the size fluctuation of the ferrite rods. Moreover, by examining the relation between the transmittance and the EMF, we can optimize the EMF to realize the best switching effect. With the retrieved effective constitutive parameters ε _eff and μ _eff obtained from the effective-medium theory, the optimal EMF can be understood in a more clear manner.     

Ionic conductivity of mixed K(NbW)O6 and KH2O(NbW)O6

The mixed oxides K(NbW)O₆ and KH₂O(NbW)O₆ were prepared by solid state reactions and characterized by X-Ray diffraction powder method, thermogravimetric analysis and differential scanning calorimetry. Electrical conductivity measurements were recorded between 190 and 508 K by the complex impedance method.     

Direct synthesis of AgInO2

Potential applications as transparent conducting oxides have made the study of ternary metal oxides based on the delafossite structure very attractive. The well known and understood thermal instability of noble metal oxides, and therefore the associated problems with high-temperature solid-state techniques to yield pure complex oxides based on noble metals, clearly illustrates the need for low-temperature alternatives. For the first time, synthesis of 3R-AgInO₂ at low temperature (175 °C) and pressure (<10 atm) was achieved by a single-step hydrothermal technique. Particle size of the orange crystallites ranged from 3 to 7 μm.     

Flame synthesis of 1-D complex metal oxide nanomaterials

One dimensional (1-D) complex metal oxide nanomaterials, such as ternary oxides, doped oxides, and hierarchical structures containing several oxides, not only benefit from large aspect ratios, but also offer exciting opportunities to design materials with desired properties by tuning their chemical compositions and tailoring their sizes and morphologies at the nanometer scale. Flame synthesis is an attractive method to grow 1-D complex metal oxide nanostructures because of its high temperature, scalability, low-cost and rapid growth rate. Here, we present three new combined flame synthesis methods: (1) simultaneous vapor–vapor growth, (2) simultaneous solid–vapor growth, and (3) sequential solid–vapor growth, to grow 1-D complex metal oxide nanostructures with well-defined compositions and morphologies. These three methods combine the previously reported flame vapor deposition and solid diffusion growth methods that were separately used to grow 1-D simple binary metal oxide nanostructures, and significantly advance the capabilities of existing flame synthesis methods for the growth of 1-D nanomaterials. The first method, simultaneous vapor–vapor growth, combines the flame vapor deposition growth of two different metal oxides by oxidizing and evaporating two different metal sources. With this we have successfully grown W-doped MoO₃ nanoplates and nanoflowers. In the second method, simultaneous solid–vapor growth, one precursor is again provided by oxidizing and evaporating metal oxide from a metal, while the other precursor diffuses out from a different growth substrate. With this we have successfully grown ternary Cu₃Mo₂O₉ nanowires. The third method, sequential solid–vapor growth, essentially uses the 1-D nanostructures firstly grown by solid diffusion as the substrates for subsequent flame vapor deposition. With this we have successfully grown hierarchical CuO/MoO₃ core/shell nanowires and MoO₃-branched CuO nanowires. We believe that these three new combined flame synthesis methods will provide a general platform for the synthesis of 1-D complex metal oxide nanostructures with tailored properties.     

The studies of structural aspects of the cluster formation in silicate glasses doped with cerium and titanium oxides by small-angle neutron scattering

The structural aspects of the formation of Ti-Ce-O nanoclusters in silicate glasses doped with oxides TiO₂ and CeO₂ have been studied by means of small-angle neutron scattering. It has been obtained that, in such glasses, complex oxide nanoclusters with sizes of 300–380 Å are formed; their average size increases and the fractal dimension is changed as the concentration of the initial oxides increases. Correlation between the structural characteristics of the nanoclusters and the optical properties of the doped silicate glasses is discussed.     

Electromotive force of a COCO2 sensor in COCO2H2H2O atmospheres and simultaneous determination of partial pressures of CO and CO2

The electromotive force (EMF) of the COCO₂ sensor using Na₂CO₃ and NASICON (Na₃Zr₂Si₂PO₁₂) as solid electrolytes has been examined in COCO₂Ar atmospheres. The EMF is related to the partial pressures of CO and CO₂ and proportional to log(P²_CO2P⁻¹_CO). The simultaneous use of the oxygen sensor of stabilized zirconia gives the EMF proportional to log(P_CO2P⁻¹_CO). The EMF's of two sensors permit to determine individually partial pressures of CO and CO₂. The existence of H₂ with high concentration does not affect the EMF's. This fact proves the applicability of the two-sensor system to the monitoring and the controlling of reducing atmospheres in industrial processes.     

Oxygen ion conductivity in doped Gd2Ti2O7 with the pyrochlore structure

Materials with the A₂B₂O₇ pyrochlore structure have interesting ionic transport properties because of their crystallographic structure, which can be described as a stable array of corner-shared BO₆ octahedra that is penetrated by a 3-dimensional tunnel configuration that is partly filled by the A₂O sublattice. The pyrochlore stochiometry means that there are built-in intrinsic oxide ion vacancies in the crystal structure in comparison to the related fluorite type structure. These are in the A₂O sublattice, so that the tunnels are only 75% occupied. The presence of these tunnels leads to the possibility of significant changes in the composition, and some ionic species in this sublattice exhibit high mobility. The cubic pyrochlore Gd₂Ti₂O₇ was doped in various ways to change its ionic and electronic transport properties. The total conductivity and partial ionic and electronic contributions were investigated by ac impedance and EMF measurement techniques. The influence of either A or B site doping with aliovalent ions that occupy sites in the A₂O and B₂O₆ sublattices was investigated. The results of these experiments are presented and discussed in relation to the crystal structure and defect chemistry of this family of oxides. Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995     

Preparation and magnetocaloric effect of (La0.67-XGdX)Sr0.33MnO3 (X =0.1,0.15) nanoparticles

We report a new route to synthesize nanosized (La_0.67-XGd_X)Sr_0.33MnO₃ (X=0.1,0.15) perovskite crystalline complex oxides at calcination temperatures of 600–900 °C using amorphous molecular alloy as precursor. The precursor could completely decompose into oxide at temperatures below 500 °C according to thermogravimetric analysis and differential thermal analysis results. X-ray diffraction demonstrated that the decomposed species was composed of perovskite structure at a calcination temperature of 600 °C for 2 h. The size and topography of the oxides are dependent on the calcination temperature of the precursor. The resulting particle size is in the range of 40–120 nm as determined by a transmission electron microscope. This method is effective and can be easily quantitatively controlled to synthesize nanosized perovskite complex oxides. The Curie temperature T_C and the magnetocaloric effect of (La_0.67-XGd_X)Sr_0.33MnO₃ (X=0.1,0.15) nanoparticles are discussed based on the measurement of the low-field magnetization curve and the isothermal magnetization curve. PACS 61.46.+w; 61.10.Nz; 75.75.+a; 81.20.Ka; 81.70.Pg     

SnO2/TiO2 mixed oxide particles synthesized in doped premixed H2/O2/Ar flames

SnO₂/TiO₂ mixed oxides with primary particle size ranging between 5 nm d_p 12 nm were synthesized by doping a H₂/O₂/Ar flame with Sn(CH₃)₄ and Ti(OC₃H₇)₄ co-currently. The effects of “flow coordinate,” concentration and flame configurations were investigated with respect to particle size and morphology of the generated mixed oxides. In situ characterization of the mixed oxides was performed using the particle mass spectrometer (PMS), while XRD, TEM, BET and UV–Vis were performed ex situ. Results obtained showed that primary particle size of mixed oxides can be controlled by varying experimental parameters. The mixed oxides have interesting properties compared to those of the pure oxides of TiO₂ and SnO₂, which were also synthesized in flames earlier. Band gap tuning opportunities are possible using mixed oxides.     

Dynamics of TiO2-based photoelectrochemical cell

The present work reports the effect of light on the open-circuit voltage of a photoelectrochemical cell (PEC) formed of TiO₂ photoanode, Pt cathode and Na₂SO₄ (0.35 M) aqueous solution as electrolyte. The studies included the measurements of the electromotive force (EMF) during the light-off and light-on cycles for the PEC involving photoanode that was made of both oxidised and reduced TiO₂ thin films. These specimens were formed by oxidation of the titanium metal at high and low oxygen activities. This was achieved by the imposition of the gas phase of two different compositions, including air, p(O₂) = 21 kPa, and the hydrogen–water vapour mixture, p(O₂) = 10^-10p({\rm O}_2) = 10^{-10} Pa, at 1,123 K and subsequent cooling to room temperature. The determined data indicate that the PEC formed of the oxidised specimen exhibits larger EMF and a substantially better stability in time. It is, therefore, concluded that the TiO₂ obtained in air exhibits superior performance-related properties compared to the reduced specimen. The obtained experimental EMF data are considered in terms of the effect of light on the reactivity of TiO₂ with oxygen and water and the related charge transfer.     

Study on ammonium acetate salt-added polyvinyl alcohol-based solid proton-conducting polymer electrolytes

Polyvinyl alcohol (PVA) complexes with different compositions of ammonium acetate (AA) are prepared by solution cast technique. Polyvinyl alcohol crystallinity decreased with increasing ammonium acetate salt content. Molecular weight and density of polyvinyl alcohol complex increased with the addition of ammonium acetate salt. The ammonium acetate salt addition resulted in plasticization and hence decreased glass transition temperature (T _g) as well as hardness number (HV). 80PVA:20AA presented maximum conductivity (σ?=?1.3?×?10^?7S cm^?1 at 303 K) with minimum activation energy (E _a) 0.151 eV below the T _g. The proton transport number determined using EMF method found ≈0.98 for polymer complex with ammonium acetate content >15 mol%. The complex impedance is measured as a function of frequency, temperature, relative humidity, and hydrogen partial pressure. Enhanced bulk conductivity with increased H₂ partial pressure and relative humidity suggested H⁺ mobility within complex polymer electrolyte.     

Hyperfine interactions in iron — Yttrium oxide systems

Hyperfine interactions of iron — yttrium oxide systems have been investigated by Mössbauer spectroscopy and magnetic measurements. The mixed oxides having varying ratios were prepared by heating the coprecipitated oxyhydroxides to about 1000°C in air. The room temperature Mössbauer spectra are complex in nature and some of them exhibit as may as 10 well resolved peaks consisting of two sets of magnetically split hyperfine six line patterns, indicating existence of two different environments around Fe. The values of specific magnetic susceptibility change with increasing amount of yttrium is maximum for 1:1 (Y:Fe) and then falls continuously. The observed H_n values are less than the reported values for α-Fe₂O₃. From the observed data it appears that a transition for the composition of 1:1 definitely takes place and probably two species are formed. Some of the mixed oxides behave like iron filings in a magnetic field.     

Application of Mössbauer spectroscopy for the complex structural analysis of iron oxide-based nanomaterials

The results of complex structural investigation by XRD, TEM, and Mössbauer spectroscopy of nanomaterials based on iron oxides Fe₃O₄ and γ-Fe₂O₃ are presented. The investigated nanomaterials include nanopowders produced chemically and nanostructural powders produced mechanochemically. The magnetic properties of the nanomaterials, measured at ambient temperature, are discussed.