Optimization of the thermoelectric properties of Bi<Subscript>2</Subscript>O<Subscript>2</Subscript>Se ceramics by altering the temperature of spark plasma sintering

The n-type polycrystalline Bi₂O₂Se ceramics were fabricated by solid state reaction and SPSed at different temperatures (873–973 K). The grains of the sample grow up gradually and the grain size enlarges from about 200 nm to micrometer level with the increase of sintering temperature. The highest electrical conductivity of 6.23 S/cm is obtained for the sample sintered at 898 K which benefits from grain orientation along (00l) plane and the highest measured density. The electrical transport properties tend to decline with further increase of the sintering temperature due to the decrease of density and the orientation degree. The maximum power factor of 78.39 μWK^?2m^?1 is obtained at 773 K. The thermal conductivity is intrinsically suppressed owing to the layered crystal structure of Bi₂O₂Se and fine grains within the nanometer size. The ZT value reaches 0.09 at 773 K for the sample SPSed at 898 K and the optimal temperature during the SPS process has been determined.     

Defect chemistry and transport properties of Pb(Zr1/2Ti1/2)O3

Abstract

In order to gain insight into the degradation mechanisms associated with ferroelectric thin films, such as fatigue and imprint, an understanding of the defect chemistry and transport properties of the material is needed. In this study several complimentary techniques have been used to either measure or calculate indirectly the various thermodynamic parameters governing defect formation and transport in Pb(Zr_1/2Ti_1/2)O₃, (PZT). By combining the results of DC equilibrium conductivity, thermoelectric power and the sealed cell techniques, “constant composition oxygen activity” and “constant composition conductivity,” values for the oxidation enthalpy (ΔH_ox), hole trapping energy (E _A) and the enthalpy of motion for holes (ΔE _A) have been determined to be ?0.49 eV, ≤0.9 eV and ≥0.1 eV, respectively. From these results, it is apparent that PZT is an oxygen excess p-type semiconductor in the experimental regime of 500°–700°C and P(O₂) ≥ 10^?4 atm. Furthermore, the results indicate that there is a significant concentration of trapped holes at high temperatures and hole conduction appears to be an activated process (i.e. small polaron conduction).     

Oxygen radical density measurement in O2–N2 gas mixture plasma by means of a thin platinum wire

The oxygen radical density was measured in a weakly ionized plasma in an O₂–N₂ gas mixture by using a simple platinum thin‐wire sensor. The increased temperatures of the platinum wire caused by the energy released in the recombination of two oxygen radicals on the platinum surface were measured by varying the nitrogen gas mixture ratio and were compared with the oxygen radical densities theoretically calculated under the same plasma conditions. The relation between the wire temperature and the oxygen radical densities was cross‐checked by quantitative measurement of oxygen radical densities with a quadrupole mass spectrometer. All of these results made it possible to determine the oxygen radical density experimentally from the platinum wire temperature alone. The influence of the ambient gas temperature on the radical density measurement is also discussed. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 149(4): 14–20, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20018     

Physicochemical and Transport Properties of Bicuvox-Based Ceramics

Polycrystalline Bi_2-xLa_xV_0.90Cu_0.10O_5.5-α (x = 0, 0.10 and 0.20) and Bi_1.90Pr_0.10V_0.90Cu_0.10O_5.5-α were prepared by the standard ceramic synthesis technique. Electrical conductivity of the Bi_1.90La_0.10V_0.90Cu_0.10O_5.5-α solid solution at temperatures above 500 K is lower in comparison with undoped BICUVOX.10, whereas transport properties of these materials at 370–450 K are close to each other. Doping Bi₂V_0.90Cu_0.10O_5.5-α with praseodymium was found to result in segregating secondary phases and decreasing conductivity and thermal expansion of the ceramics. Oxygen ion transference numbers of the oxides with moderate rare-earth dopant content (x ≤ 0.10) vary in the range of 0.90–0.99 at 780–910 K, decreasing with increasing temperature. Thermal expansion coefficients of Bi_2-xLn_xV_0.90Cu_0.10O_5.5-α ceramics were calculated from the dilatometric data to be (16.1–18.0) × 10^-6K^-1 at 730–1050 K.     

Thermodynamic,transport and radiation properties of high-temperature CF3I and transient conductance of residual arc sustained in axial CF3I flow

The present paper reports fundamental properties of CF₃I under high-temperature conditions to find out the usefulness of CF₃I as an arc-quenching gas. Firstly, particle compositions of CF₃I were theoretically calculated in a temperature range from 300 to 30 000 K. Secondly, thermodynamic, transport and radiation properties of the CF₃I were also obtained for pressures 0.1–1.0 MPa. Finally, the transient process of a conductance of a residual arc in CF₃I was derived to compare with those in other arc-quenching gases. In addition, an arc extinguishing capability of CF₃I in a thermal re-ignition region was derived to find out whether CF₃I shows a higher capability than CO₂, N₂ and air. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Characteristics evaluation of a CO2‐capturing power generation system with reheat cycle utilizing regenerative oxygen‐combustion steam‐superheater

A new CO₂‐capturing power generation system is proposed that can be easily realized by applying conventional technologies. In the proposed system, the temperature of medium‐pressure steam in a thermal power plant is raised by utilizing an oxygen‐combusting regenerative steam‐superheater. The CO₂ generated by combusting the fuel in the superheater can be easily separated and captured from the exhaust gas at the condenser outlet, and is liquefied. The superheated steam is used to drive a steam turbine power generation system. Using a high‐efficiency combined cycle power generation system as an example, it is shown that the proposed system can increase the power output by 10.8%, and decrease the CO₂ emissions of the entire integrated system by 18.6% with a power generation efficiency drop of 2.36% compared with the original power plant without CO₂ capture, when the superheated steam temperature is 750 ^°C. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(1): 35–41, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20575     

Influence of system operation method on CO2 emissions of PV/solar heat/cogeneration system

A PV/solar heat/cogeneration system is assumed to be installed in a hotel. The system is operated with various operation methods: CO₂ minimum operation, fees minimum operation, seasonal operation, daytime operation, and heat demand following operation. Of these five operations, the former two are virtual operations that are operated with the dynamic programming method, and the latter three are actual operations. Computer simulation is implemented using hourly data of solar radiation intensity, atmospheric temperature, electric, cooling, heating, and hot water supply demands for one year, and the life‐cycle CO₂ emission and the total cost are calculated for every operation. The calculation results show that the two virtual and the three actual operations reduce the life‐cycle CO₂ emission by 21% and 13% compared with the conventional system, respectively. In regard to both the CO₂ emission and the cost, there is no significant difference between the two virtual operation methods or among the three actual operation methods. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(2): 54–63, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20414     

Effect of magnetic field strength and admixture gas on current interrupting capability of a CO2 rotary‐arc load‐break switch

First, current interrupting experiments were performed for a rotary‐arc type of load‐break switch filled with pure CO₂ at a total pressure of 0.1 MPa. Increase in the coil turns for generating magnetic field from 1 to 1.8, 2.5, and 3.6 (arbitrary unit) raised the current interrupting capability from 2.6 kA to 3.2, 3.5, and 4.1 kA. Second, experiments were performed for CO₂ gas mixture under the condition of 3.6 coil turns. Gases of He, O₂, N₂, and air were admixted to CO₂. Adding either He or O₂ to CO₂ at a concentration of 30% allows the switch to have higher interrupting capability than using pure CO₂. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(2): 21–27, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20742     

Thermal Conductivity of Nano ZnO Doped CaFe2O4

The research objective of this study was to examine whether Zn was an effective doping element for thermal conductivity. Ca_1-xZn_xFe₂O₄ (x = 0.0–0.5) were synthesized by solid state reaction method. The XRD results showed that all samples were mixed phase of CaFe₂O₄ and ZnFe₂O₄. The structure of Ca_1-xZn_xFe₂O₄ (x = 0.0–0.5) belonged to a group of an orthorhombic system (space group: Pbnm). It was observed that all the samples of Ca_1-xZn_xFe₂O₄ (x = 0.0–0.5) had positive Seebeck coefficient as shown on p-type semiconductor behavior. Thus thermal conductivity tended to decrease with increasing x value. The Ca_0.6Zn_0.4Fe₂O₄ showed lowest thermal conductivity of 6.52 W m^?1 K^?1 at 473 K, which was lower than 50.81% of CaFe₂O₄. These results suggested that Zn was an effective doping element for improving the thermal conductivity of Ca_1-xZn_xFe₂O₄.     

Startup analysis of an H2‐O2‐fired gas turbine cycle

A new thermodynamic cycle using artificial energy is now under investigation. The Japanese World Energy Network research program (WE‐NET) is one of the artificial energy technology programs which will use hydrogen energy. One of the targets of the program is the development of a high‐thermal‐efficiency, emission‐free power plant. The H₂‐O₂‐fired gas turbine is the key technology of the program and the advanced Rankine cycle is suggested as one of the most effective cycles. The advanced Rankine cycle is based on the direct steam expansion cycle. Mass and heat balance calculations were performed to determine the optimal operating point and the component design was carried out to develop the cycle. Further investigations necessary to realize the cycle include such topics as operational ability and cost performance. This paper considers operational ability, especially startup performance. In this analysis, the algorithm and process flow configuration for startup are developed. The investigation finds that the advanced Rankine cycle has good potential for practical use. © 1999 Scripta Technica, Electr Eng Jpn, 128(1): 9–16, 1999     

Study of DC circuit breaker of H2‐N2 gas mixture for high voltage

Global warming caused by such gases as CO₂ is a subject of great concern. Automobile emissions are an especially great problem in this respect. Therefore, hybrid cars are being widely developed and used. Because hybrid cars use electric power and gasoline, their emissions of CO₂ are reduced. The electric motor of a hybrid car is driven by a battery, which has large capacity. Therefore, relays must interrupt a high DC current on switching between the electric motor and the gasoline engine, and hydrogen gas‐filled relays are used for the purpose. In interruption tests in which we investigated the basic characteristics of hydrogen gas, the DC current did not reach a current‐zero point. Thus, the current must be coerced to zero by using a high arc voltage. The loss coefficient and arc voltages of hydrogen are high, and we therefore performed interruption tests using a high arc voltage. Interruption tests and dielectric breakdowns test of air, pure hydrogen, and a hydrogen‐nitrogen mixture indicated that an 80%–20% H₂–N₂ mixture is the most effective. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(2): 9–17, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21042     

PD time‐sequential properties of SF6 and SF6 gas mixture including CO2

This paper deals with partial discharge (PD) time‐sequential properties of SF₆/N₂/CO₂ ternary gas mixture as well as SF₆ and SF₆/N₂ gas mixture under AC and positive DC voltage applications. The measurements were carried out by changing the gas pressure up to 0.6 MPa and applied voltage with the N‐shape characteristics of breakdown voltage versus gas pressure for each tested gas considered. We obtained experimental results of the gas pressure dependence of maximum peak value of PD current pulse as well as the relationship between the time interval of PD pulses and the peak value of PD pulse. We discuss the mechanism of increase in breakdown voltage by adding CO₂ into SF₆/N₂ gas mixtures in terms of change of PD type from streamer to leader discharge. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(3): 32–40, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20073     

Crystal structure and the effect of annealing atmosphere on the dielectric properties of the spinels MgAl2O4, NiFe2O4, and NiAlFeO4

The non-transition metal spinel MgAl₂O₄ and the transition metal spinels (NiFe₂O₄, NiAlFeO₄) have been prepared by standard ceramic processing method in the air. The effect of annealing atmosphere on the dielectric properties after sintering has been studied. The annealing atmospheres were N₂, O₂, and N₂–H₂ mixture. Dielectric constant ? _r and tangent loss tanδ have been characterized by varying the measuring temperature and frequency (5 Hz–5 MHz) using the impedance analyzer. The ? _r and tanδ of the non-transition metal spinel MgAl₂O₄ remained unchanged even with varying the annealing atmosphere. While the dielectric properties of the transition metal spinels, NiFe₂O₄ and NiAlFeO₄ were critically dependent on the annealing atmosphere. Crystal structural models for the samples manufactured in air have been tested by the Rietveld refinement method for both the centrosymmetric Fd-3m and the noncentrosymmetric F-43m. The electron density distributions were determined by the whole pattern fitting based on the maximum entropy method (MEM). The dielectric properties of the samples have been also discussed in terms of the structure and electron distribution analysis results.     

Simplified Analytical Treatment of Defect Equilibria: Applications to Oxides with Multivalent Dopants

A simplified analytical treatment of rather complex defect equilibria involving systems with multivalent dopants is presented. This approach is first demonstrated for the case of Gd₂Ti₂O₇; doped with multiple valent donors, in which the effects of variations in donor ionization levels and in the equilibrium constants on the defect equilibria are examined. The conductivity data of U doped CeO₂ are then evaluated, leading to equilibrium constants in good agreement with previous results, but allowing a more complete analysis.     

Insulation properties of a CO2/N2 50% SF6 gas mixture in a nonuniform field

This paper describes partial discharge (PD) inception and breakdown voltage characteristics of a CO₂/N₂/SF₆ gas mixture in a nonuniform field. These voltage characteristics were investigated with ac high voltage by changing the mixture rate of each gas of CO₂, N₂, and SF₆ gas and the gas pressure from 0.1 MPa to 0.6 MPa. It was found that adding a small amount of CO₂ gas into a N₂/SF₆ mixture causes a drastic increase in the breakdown voltage. For instance, when the mixture rate of SF₆ in N₂/SF₆ gas mixture is 50%, with the addition of 1% CO₂ the maximum breakdown voltage becomes 1.31 and 1.15 times higher than that of a 50% N₂/50% SF₆ gas mixture and pure SF₆ gas, respectively. Moreover, those voltage characteristics of a CO₂/N₂/SF₆ gas mixture were also investigated by changing the electric field utilization factor as well as by applying positive and negative standard lightning impulse voltages in order to discuss the corona stabilization effect, which seems to be one reason for the drastic increase in the breakdown voltage. These results and breakdown mechanism of the CO₂/N₂/SF₆ gas mixture are discussed on the basis of the corona stabilization effect and the dissociation energies of the component gases by observing PD light images, PD light intensities through a blue and red filter, and PD current waveforms. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(3): 34–43, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10019     

Predication of Thermal Conductivity of Mg2X (X = Ge and Sn) by Molecular Dynamics

Molecular dynamics (MD) simulations of elastic and thermal properties of Mg₂X (X = Ge and Sn) based on anti-fluorite structure (CaF₂) at temperature range 300?700 K were presented. The MD simulation in this study involving the Morse?type potential functions, and the Busing–Ida potential to determine the interatomic interaction among cluster atoms size 4×4×4 unit cells of 768 atoms {512?Mg^1.2+, 256?(Ge, Sn)^2.4?}. The potential parameter functions of the cluster atoms were indicated by random numerical method and fit lattice parameter from the experimental data obtained at room temperature. The calculation of lattice parameter, pressure, temperature and energy contributes to evaluation of the elastic properties. The results showed that Mg₂Ge had better elasticity than Mg₂Sn. On the other hand, Mg₂Sn had less thermal conductivity than Mg₂Ge. Since thermal conductivity decreases with increasing temperature, the interesting feature of thermal conductivity is particulary useful to enhance thermoelectric performance of materials.     

CO2 Sensing Property of CuO-BaTiO3 Mixed Oxide Film Prepared by Self-Assembled Multibilayer Film as a Precursor

Preparation of CuO-BaTiO₃ mixed oxide thin film by the decomposition of a self-assembled multibilayer film as a molecular template was investigated in this study. Furthermore, CO₂ sensing property of the resultant thin film was investigated as a capacitive type sensor. The self-assembled bilayer film of few 1000 layers thickness can be obtained easily by casting an aqueous suspension consisting of dimethyldihexadecylammoiun bromide (DC1-16), Cu(ClO₄)₂, Ba(TiO(C₂H₄)₂), 2,6-dimetyle-3,5heptadione (DHP), and polyvinyl alcohol. Divalent copper ion (Cu²⁺)) which is associated with 2 DHP molecules was incorporated into the molecular bilayer film and BaTiO₃ precursor exists at the interspace of molecular bilayer film by coordinating with polyvinyl alcohol. Upquenching the organic-inorganic film at 1173 K leads to the uniform film of CuO-BaTiO₃ oxide mixture. Although operating temperature shifted to higher temperature, the resultant film exhibits the capacitance change upon exposure to CO₂. Consequently, it is concluded that the mixed oxide film of CuO-BaTiO₃ prepared by the decomposition of multibilayer film was also an appropriate capacitive type CO₂ sensor.     

Mixed Hydroxide Precursors for La2Ti2O7 and Nd2Ti2O7 by Homogeneous Precipitation

Feasibility of formation of stoichiometric precursors of either M₂ (TiO)₂(C₂O₄)₅ 4H₂O (M = La and Nd) or coprecipitated hydroxides of M(OH)₃+TiO(OH)₂ was investigated by two solution routes at different pH values. Composition of precipitates obtained at pH = 7.0 by coprecipitation method starting from La or Nd nitrates and potassium titanyl oxalate corresponded to a physical mixture of La or Nd(C₂O₄)₃ 9.5H₂O and TiO(OH)₂7·H₂O which on thermal decomposition did not yield phase pure M₂Ti₂O₇. However, precipitation from La or Nd nitrates and titanium tertrachloride by urea hydrolysis yielded homogeneous mixture of hydroxides of La or Nd and Ti, which on pyrolysis at 950°C yielded phase pure La₂Ti₂O₇ and Nd₂Ti₂O₇. Use of potassium titanyl oxalate as precursor for Ti, led to selective precipitation of La or Nd oxalate even at pH as low as 0.1 leading to sequential precipitation of La or Nd oxalate followed by Ti hydroxide at pH = 3.0. The resultant precipitate on pyrolysis underwent typical solid-state reaction.     

Structural, luminescent, and NO2 sensing properties of SnO2-core/V2O5-shell nanorods

SnO₂-core/V₂O₅-shell nanorods were synthesized using a two-step process: thermal evaporation of Sn powders and sputter-deposition of V₂O₅. The core-shell nanorods were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and photoluminescence spectroscopy. The diameters of these core-shell nanorods ranged from 80 to 200 nm with a shell layer thickness in the range of 7–13 nm. The cores and shells of the annealed core-shell nanorods consisted of a single crystal tetragonal-structured SnO₂ and a single crystal orthorhombic-structured V₂O_5, respectively. Photoluminescence measurements revealed the SnO₂ nanorods to have a yellow emission band centered at approximately 590 nm, which was enhanced significantly by the V₂O₅ coating and further by thermal annealing. The sensitivity of the networked SnO₂-core/V₂O₅-shell nanorod sensor to NO₂ gas was slightly higher than that of the bare SnO₂ nanorod sensor. The enhanced sensitivity of the SnO₂ nanorods by the V₂O₅ coating was attributed to the modulation of electron transport by the SnO₂-V₂O₅ heterojunction with an adjustable energy barrier height.     

Microelectrodes for local conductivity and degradation measurements on Al stabilized Li<Subscript>7</Subscript>La<Subscript>3</Subscript>Zr<Subscript>2</Subscript>O<Subscript>12</Subscript> garnets

The attractiveness of Li₇La₃Zr₂O₁₂ (LLZO) cubic based garnets lies in their high ionic conductivity and the combination of thermal and electrochemical stability. However, relations between composition and conductivity as well as degradation effects are still not completely understood. In this contribution we demonstrate the applicability of microelectrodes (Ø = 20–300 μm) for electrochemical impedance spectroscopy (EIS) studies on LLZO garnets. Microelectrodes allow to obtain local information on the ionic conductivity. A comparison between the overall performance of the sample (3.3 × 10^?4 S cm^?1) and local measurements revealed differences in conductivity with a maximum of the locally measured values of 6.3 × 10^?4 S cm^?1 and a minimum of 2.6 × 10^?4 S cm^?1. One reason behind these conductivity variations is most probably a compositional gradient in the sample. In addition, microelectrodes are very sensitive to conductivity changes near to the surface. This was used to investigate the effect of moisture in ambient air on the conductivity variations of LLZO. Substantial changes of the measured Li-ion transport resistance were found, particularly for smaller microelectrodes which probe sample volumes close to the surface.