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Microstructural characterization and electrical properties of spray pyrolyzed conventionally sintered or hot-pressed BaZrO3 and BaZr0.9Y0.1O3 − δ

Authors Paul Inge Dahl, Hilde Lea Lein, Yingda Yu, Julian Tolchard, Tor Grande, Mari-Ann Einarsrud, Christian Kjlseth, Truls Norby and Reidar Haugsrud
Source
Solid State Ionics
Volume: 182, Issue: 1, Pages: 32-40
Time of Publication: 2011-02
Abstract A spray pyrolysis route to BaZrO3 (BZ) and BaZr0.9Y0.1O2.95 (BZY) powders was developed starting from nitrate solutions. Homogeneous powders with a grain size of ~ 100 nm were achieved. A calcination of the powder was necessary to remove carbonates formed during the spray pyrolysis. Hot pressing was in comparison with conventional sintering more effective to enhance densification and suppress grain growth, and dense (> 96%) materials with homogeneous microstructure were obtained. The Y-substitution decreased the densification rate. Minor amounts of a secondary phase was observed at the grain boundary triple points of BZY, but the grain boundaries were otherwise found to be coherent and without significant secondary phase accumulation. Impedance spectroscopy vs T, pO2 and pH2O of conventionally sintered BZ and hot-pressed BZY demonstrated that the conductivity of BZ was orders of magnitude lower than compared to BZY. The conductivity of BZ displayed mixed proton and p-type electronic conduction characteristics in the grain interior which was depressed at the grain boundaries. The grain boundaries showed an additional n-type electronic conduction under reducing conditions. The conductivity characteristics were according to core-space charge layer theory. BZ seems to exhibit a larger ratio of p-type electronic to protonic conduction as compared to BZY, contrary to the prediction of simple defect chemistry.

BiFeO3–PbZrO3–PbTiO3 ternary system for high Curie temperature piezoceramics

Authors Wei Hu, Xiaoli Tan and Krishna Rajan
Source
Journal of the European Ceramic Society
Volume: 31, Issue: 5 Time of Publication: 2011-05
Abstract BiFeO3–PbZrO3–PbTiO3 ternary solid solution system was investigated for the development of piezoelectric ceramics with high Curie temperatures. The search for the morphotropic phase boundary (MPB) compositions in this ternary system started from mixing two MPB compositions: 0.70BiFeO3–0.30PbTiO3 and 0.52PbZrO3–0.48PbTiO3. The content of PbTiO3 was then further fine tuned in order to reach the appropriate volume fraction between the rhombohedral and tetragonal phases in the sintered ceramics. It was observed that the sintering temperature has a profound impact on the density, grain morphology, dielectric and ferroelectric properties of the ceramics. The composition that displays the best combined structure and properties was identified to be 0.648BiFeO3–0.053PbZrO3–0.299PbTiO3, with a Curie temperature TC of 560 C, a remanent polarization Pr of 15.0 μC/cm2, and a piezoelectric coefficient d33 of 64 pC/N.

Synthesis and characterization of Ca-substituted YAlO3 by pechini route for solid oxide fuel cells

Authors Ramya Hariharan, Prakash Gopalan
Source
Solid State Sciences
Volume: 13, Issue: 1, Pages: 168-174
Time of Publication: 2011-01
Abstract The high operating temperature requirement of solid oxide fuel cells demands electrolyte materials stable at temperatures around 800 C. The perovskite material YAlO3, with yttrium ion on the A-site and the aluminium ion on the B-site is being investigated as an electrolyte for solid oxide fuel cells. This work investigates the structure and electrical conductivity of undoped and Ca-doped YAlO3 compositions that has been synthesized by the Pechini route. The samples have been investigated by X-ray diffraction studies. The electrical conductivity studies have been performed using a.c impedance spectroscopy in the range 200–800 C in air. The doped YAlO3 of composition x = 0.1 exhibits a total conductivity of about 2.2 mS/cm at 800 C. The microstructural evaluation of the samples has been conducted by scanning electron microscopy coupled with energy dispersive spectrum analysis.

δ-Phase to defect fluorite (order–disorder) transition in the R2O3–MO2 (R = Sc; Tm; Lu; M = Zr; Hf) systems

Authors A.V. Shlyakhtina, D.A. Belov, S.Yu. Stefanovich, I.V. Kolbanev, O.K. Karyagina, A.V. Egorov, S.V. Savilov and L.G. Shcherbakova
Source
Materials Research Bulletin
Volume: 46, Issue: 4, Pages: 512–517
Time of Publication: 2011-04
Abstract We have studied the δ-phase to defectfluoriteF* (order–disorder) transition in the R4M3O12 (R = Sc, Tm, Lu; M = Zr, Hf) compounds. The temperature of the δ–F* phasetransition in Tm4Zr3O12 is ∼1600 C. The rate of this transition in R4Zr3O12 (R = Sc, Tm, Lu) decreases markedly with decreasing difference in ionic radius between the R3+ and Zr4+, leading to stabilization of the δ-phasesR4Zr3O12 with R = Sc and Lu at high temperatures (∼1600 C). During slow cooling (5 C/h), the high-temperature defectfluoritesF*-R2Hf2O7 (R = Tm, Lu) decompose reversibly to form the δ-phasesR4Hf3O12. Some of the materials studied exhibit microdomains formation effects, typical of the fluorite-related oxide compounds in the R2O3–MO2 (M = Ti, Zr, Hf) systems of the heavy rare earths. The high-temperature defectfluoritesF*-R4M3O12 (R = Tm, Lu; M = Zr, Hf) as a rule contain antiphase microdomains of δ-R4Zr3O12. After slow cooling (5 C/h), such microdomains are large enough for the δ-phase to be detected by X-ray diffraction. The conductivity data for R4M3O12 (R = Sc, Tm, Lu; M = Zr, Hf) and Ln2Hf2O7 (Ln = Dy, Lu) prepared by different procedures show that the rhombohedral phasesδ-R4M3O12 (R = Sc, Tm, Lu; M = Zr, Hf) are poorer conductors than the defectfluorites, with 740 C conductivity from 10−6 to 10−5 S/cm. The conductivity drops with decreasing rare-earth ionic radius and, judging from the Ea values obtained (1.04–1.37 eV), is dominated by oxygen ion transport. The highest conductivity, ∼6 10−4 S/cm at 740 C, is offered by the rapidly cooled F*-Dy2Hf2O7. In the fluorite homologous series, oxygen ion conductivity decreases in the orderdefect pyrochlore > defectfluorite > δ-phase.
Keywords Fluorite; δ-Phases R4M3O12; Pyrochlore; Order–disorder transition; Antiphase microdomains; High-temperature conductivity
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Polymorphism and high-temperature conductivity of Ln2M2O7 (Ln = Sm─Lu; M = Ti, Zr, Hf) pyrochlores

Authors A.V. Shlyakhtina, L.G. Shcherbakova
Source
Solid State Ionics
Volume: 192, Issue: 1, Pages: 200–204
Time of Publication: 2011-06
Pyrochlore; Fluorite; Order─disorder; Defects; High-temperature conductivity; Ionic conductivity; Solid electrolyte

Proton conductivity in Sm2Sn2O7 pyrochlores

Authors K.E.J. Eurenius, E. Ahlberg and C.S. Knee
Source
Solid State Ionics
Volume: 181, Issue: 35-36, Pages: 1577-1585
Time of Publication: 2010-11
Abstract The electrical conductivity of the pyrochlore systems, Sm2Sn2O7, Sm1.92Ca0.08Sn2O7 − δ and Sm2Sn1.92Y0.08O7 − δ was studied using impedance spectroscopy under wet and dry gas (O2 and Ar) in the temperature range 150–1000 C. Enhancements of the bulk conductivity of all samples at temperatures up to ~ 550 C were observed for wet conditions consistent with significant levels of proton conduction. The presence of dissolved protons in the acceptor-doped materials, Sm1.92Ca0.08Sn2O7 − δ and Sm2Sn1.92Y0.08O7 − δ, is supported by infrared spectroscopy and thermogravimetric analysis. Proton conduction was confirmed by isotope effects under heavy water (O2/D2O and Ar/D2O). The A-site substituted sample Sm1.92Ca0.08Sn2O7 − δ yielded the highest levels of proton conduction and displayed mixed ionic and electronic conduction under dry oxidising conditions. Electron hole conduction dominates in dry oxygen for Sm2Sn1.92Y0.08O7 − δ and Sm2Sn2O7. For the A-site doped sample bulk and grain boundary conduction could be separated. The specific grain boundary conduction was calculated using the brick layer model and was found to be two orders of magnitude lower compared to the bulk conductivity. The unexpected increase in conductivity seen for the undoped sample under wet gas is discussed in the context of structural disorder and possible filling of the un-occupied anion site in the pyrochlore structure by OH-groups.
Keywords Sm2Sn2O7; Proton conductor; Pyrochlore; Oxide ion conductivity; p-type conductivity; Infra-red spectroscopy; Thermogravimetric analysis

Experimental and theoretical studies of hydrogen permeation for doped strontium cerates

Authors Maki Matsuka, Roger D. Braddock, Hiroshige Matsumoto, Takaaki Sakai, Igor E. Agranovski and Tatsumi Ishihara
Source
Solid State Ionics
Volume: 181, Issue: 29-30, Pages: 1328-1335
Time of Publication: 2010-09
Abstract Non-galvanic hydrogen permeation properties of SrCe0.95Yb0.05O3 − α (SCYb-5) and SrCe0.95Tm0.05O3 − α (SCTm-5) dense membranes were investigated in a ‘wet’ hydrogen atmosphere where water vapour partial pressures were well defined and monitored for the entire duration of the experiments. The theoretical modelling of hydrogen permeation flux for SCYb-5 and SCTm-5 was also undertaken, and compared with experimental results. The parameter tuning was also performed by fitting the model to the experimental data obtained in this study. The experimental hydrogen permeation flux for SCYb-5 and SCTm-5 dense membranes was 6.8e− 9 mol/cm2/s and 7.1e− 9 mol/cm2/s, respectively, under the upstream hydrogen partial pressure of 0.25 atm (25%H2/Ar) at 900 C. As expected, the hydrogen permeation flux increases with the increase in the upstream hydrogen partial pressures, reaching the maximum flux of 1.4e− 8 mol/cm2/s and 1.6e− 8 mol/cm2/s, for SCYb-5 and SCTm-5 respectively, under the upstream hydrogen partial pressure of 1 atm (100%H2) at 900 C. Previous modelling used hydrogen permeation data collected by others in a permeation test conducted in a ‘dry’ hydrogen atmosphere (with unknown water vapour pressures). The modelled hydrogen permeation flux agreed well with the experimental data attained in this study, for both SCYb-5 and SCTm-5 samples. The parameter tuning further improved the model predictions for those samples. It was apparent that the modelled hydrogen flux agreed better with the experimental data obtained in this study (i.e. in a wet hydrogen atmosphere with known water vapour pressures).
Keywords Dense ceramic membranes; Hydrogen permeation; Modelling

Directed integration of ZnO nanobridge sensors using photolithographically patterned carbonized photoresist

Authors Chien-Chih Huang, Brian D Pelatt and John F Conley Jr
Source
Nanotechnology
Volume: 21, Issue: 19 Time of Publication: 2010-05
Abstract A method for achieving large area integration of nanowires into electrically accessible device structures remains a major challenge. We have achieved directed growth and integration of ZnO nanobridge devices using photolithographically patterned carbonized photoresist and vapor transport. This carbonized photoresist method avoids the use of metal catalysts, seed layers, and pick and place processes. Growth and electrical connection take place simultaneously for many devices. Electrical measurements on carbonized photoresist/ZnO nanobridge/carbonized photoresist structures configured as three-terminal field effect devices indicate bottom gate modulation of the conductivity of the n-type ZnO channel. Nanobridge devices were found to perform well as ultraviolet and gas sensors, and were characterized as regards ultraviolet light pulsing, oxygen concentration, and humidity. The sensitivity of the three-terminal nanobridge sensors to UV light and oxygen was enhanced by application of a negative bottom gate voltage.

Yttria-stabilized zirconia thin film electrolyte produced by RF sputtering for solid oxide fuel cell applications

Authors Federico Smeacetto, Milena Salvo, Lakshmi Chandru Ajitdoss, Sergio Perero, Tomasz Moskalewicz, Stefano Boldrini, Lioudmila Doubova and Monica Ferraris
Source
Materials Letters
Volume: 64, Issue: 22, Pages: 2450-2453
Time of Publication: 2010-11
Abstract Thin film (40–600 nm) yttria-stabilized zirconia (YSZ) electrolytes for solid oxide fuel cells (SOFC) were deposited on NiO-YSZ anodes and fused silica substrates by RF sputtering, using low applied power without the use of post deposition annealing heat treatment. YSZ film showed a nanocrystalline structure and consisted of the Zr.85Y.15O1.93 (fcc) phase. The film was dense and the YSZ/anode interface was continuous and crack free. According to preliminary in-plane conductivity measurements (temperature range 550–750 C) on the YSZ film, the activation energy for ionic conduction was found to be 1.18 0.01 eV.
Keywords Thin films; Ceramics; Microstructure; Nanomaterials

High-temperature proton conductivity and defect structure of TiP2O7

Authors Vajeeston Nalini, Reidar Haugsrud and Truls Norby
Source
Solid State Ionics
Volume: 181, Issue: 11-12, Pages: 510-516
Time of Publication: 2010-04
Abstract Nominally undoped TiP2O7 and TiP2O7 with 2 mol-% substitution of Ti by Al were synthesized from TiO2 (Al2O3) and H3PO4(aq), sintered at 1050 C, and characterized by XRD, TEM and SEM. The electrical conductivity was investigated at 300–1000 C as a function of p(O2), p(H2O), and p(D2O). The material's phase transition around 700 C is clearly visible in the conductivity curves. Al substitution hardly increased the conductivity. The conductivity was higher in H2O- than in D2O-containing and dry atmospheres, indicating the dominance of proton conduction. The conductivity was accordingly mainly independent of p(O2). A slight increase in the conductivity with decreasing p(O2) at the highest temperatures was indicative of a minor contribution of n-type electronic conduction. The p(H2O) and temperature dependencies of the conductivity have been modelled as a sum of proton and electron partial conductivities under a situation with protons charge compensated by oxygen interstitials as dominating defects.
Keywords Titanium pyrophosphate; TiP2O7; Al-substituted TiP2O7; Proton conduction; Defect structure

Scandium stabilized zirconium thin films formation by e-beam technique

Authors Darius Virbukas, Giedrius Laukaitis, Julius Dudonis, Oresta Katkauskė and Darius Milčius
Source
Solid State Ionics
Volume: 184, Issue: 1, Pages: 10–13
Time of Publication: 2011-03
Abstract Scandiumstabilizedzirconium (10ScSZ) thin ceramic films were deposited by e-beam evaporation of (ZrO2)0.90(Sc2O3)0.10 micro powder (particle size 0.5 0.7 μm). The influence of deposition rate on formed thinfilms microstructure and electrical properties was studied. 10ScSZ thinfilms were deposited on two types of different substrates: optical quartz (SiO2) and Alloy-600 (Fe–Ni–Cr) substrates. Deposition rate was changed from 2 to 16 /s to test its influence on thinfilmformation and its properties. The microstructure of formed 10ScSZ thin ceramic films was studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Electrical parameters of formed thin ceramics were investigated in the frequency range from 0.1 Hz to 1.0 MHz (in temperature range from 473 to 873 K). The ionic conductivity of the deposited electrolyte 10ScSZ thinfilms was determined by impedance spectroscopy. It was determined that the deposition rate (in range from 2 to 16 /s) has influence on crystallite size. It increases by increasing the deposition rate from 18.4 to 26.9 nm. The XRD measurements show that the formed 10ScSZ thinfilms do not repeat the crystallographic phase of the initial evaporated powder material—it is changes from rhombohedra (initial powder) to cubic (the formed thinfilms).
Keywords Scandium stabilized zirconium (ScSZ); Ionic conductivity; Electron beam deposition; Solid oxide fuel cells (SOFC)
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Effect of sintering temperature and sintering additives on ionic conductivity of LiSi2N3

Authors Eiichirou NARIMATSU, Yoshinobu YAMAMOTO, Toshiyuki NISHIMURA and Naoto HIROSAKI
Source
Journal of the Ceramic Society of Japan
Volume: 118 , Issue: 1381 , Pages: 837-841
Time of Publication: 2010-09
Abstract The effect of sintering temperature and sintering additives on the ionic conductivity of LiSi2N3 was studied by performing complex impedance measurements. LiSi2N3 materials were fabricated by the reaction of Li3N, Si3N4, and sintering additives at temperatures of 1873–2073 K. Dense hot-pressed bodies were obtained at 1973–2073 K in the case of undoped LiSi2N3 and at 1873 K in the case of Y2O3, CaF2, and B2O3 addition. The ionic conductivity increased greatly with increasing sintering temperature and exhibited a strong dependence on the type of sintering additive. When the sintering temperature was constant at 1873 K, although the conductivities of Y2O3-doped LiSi2N3 and CaF2-doped LiSi2N3 were lower than that of undoped LiSi2N3, the conductivity of B2O3-doped LiSi2N3 was higher than that of undoped LiSi2N3. The enhanced conductivity of B2O3-doped LiSi2N3 can be attributed to the increase in the density of the sintered material without the formation of a phase of significant resistance at the grain boundaries.
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Defects and transport properties of Sr-doped LaP3O9

Authors Vajeeston Nalini, Reidar Haugsrud and Truls Norby
Source
Solid State Ionics
Volume: 181, Issue: 27-28, Pages: 1264-1269
Time of Publication: 2010-09
Abstract LaP3O9 and 2 mol-% Sr-doped LaP3O9 have been synthesized by the solid-state reaction method and the phase purity was characterized by powder X-ray diffraction and scanning electron microscopy. The AC conductivity of sintered disks was measured with two-point electrode setup in the temperature range 300 − 700 C under oxidizing and reducing conditions at different oxygen and water vapor (H2O or D2O) partial pressures by means of impedance spectroscopy. The water vapor dependency and isotope effect reveal that protons are the predominant charge carrier. The conductivity was mainly independent of the partial pressure of oxygen at all measured temperatures under both oxidizing and reducing conditions, suggesting only minor electronic conductivity. Hydration thermodynamics and transport parameters for the Sr-doped sample have been determined based on a defect chemical model applied to thermogravimetry and conductivity data.
Keywords Proton conductivity; LaP3O9; Sr-doped LaP3O9; Defect structure; Thermodynamic relations; Transport parameters

Charge carriers in grain boundaries of 0.5% Sr-doped LaNbO4

Authors Harald Fjeld, Despoina Maria Kepaptsogloub, Reidar Haugsrud and Truls Norby
Source
Solid State Ionics
Volume: 181, Issue: 3-4, Pages: 104-109
Time of Publication: 2010-02
Abstract The grain boundary and grain interior conductivities of La0.995Sr0.005NbO4 − δ have been studied by means of impedance spectroscopy at 400 C after quenching from different pH2O, pO2 and temperatures. Effects of H/D isotope shifts on the conductivity were, moreover, determined from 400 to 480 C under isothermal conditions. The microstructure and composition were characterized by scanning electron microscopy and transmission electron microscopy. On basis of the effects of pH2O and H/D isotope exchange on the grain boundary and grain interior conductivities, it is concluded that protons are the major charge carrier and, furthermore, that they are relatively more predominating in the grain boundaries than in the grain interior. Ionic transport in the grain boundaries is discussed in terms of the grain boundary core–space charge layer model.
Keywords LaNbO4; Grain boundaries; Impedance spectroscopy; TEM; Space charge effects

Electrical Properties and Gas Sensing Characteristics of the Al2O3/4H SiC Interface Studied by Impedance Spectroscopy

Authors Pawel A. Sobas, Ola Nilsen, Helmer Fjellvg, Bengt G. Svensson
Source
Materials Science Forum
Silicon Carbide and Related Materials 2009
Volume: 645 - 648, Pages: 531-534
Time of Publication: 2010-04
Abstract Using impedance spectroscopy (IS) for characterization of the electrical properties and gas sensing characteristics of Al2O3/4H-SiC (MOS) structures, insight on the capacitive and resistive contributions in the interfacial region of the MOS structures is obtained. Applying DC bias voltages between accumulation and depletion (corresponding to the interfacial region) allows investigation of the voltage shift of the capacitance versus voltage (CV) curve at different temperatures and atmospheres. This voltage shift forms the basis to use the MOS structure as a gas sensor. The MOS capacitance, as extracted from IS data, is different from the one obtained using CV measurements, due to the ability of distinguishing the resistive contribution (using IS). Voltage shifts between 1 and 2 V are clearly revealed during exposure to hydrogen and oxygen, and this shift exhibits a long-term stability of operation at temperatures up to 500C. Hence, Al2O3 exhibits great promise as a gate dielectric in MOS-based gas detecting devices for use at elevated temperatures.
Keywords Impedance Spectroscopy, MOS Capacitor

Improved Proton Conductivity in Spark-Plasma Sintered Dense Ceramic BaZr0.5In0.5O3−delta

Authors Istaq Ahmed, Francis G. Kinyanjui, Patrick Steegstra, Zhijian J. Shen, Sten-G. Eriksson, and Mats Nygren
Source
Electrochem. Solid-State Lett.
Volume: 13, Issue: 11, Pages: B130-B134
Time of Publication: 2010-11
Abstract Spark-plasma sintering method was used to prepare dense proton conducting perovskite oxide BaZr0.5In0.5O3−delta. Analysis of X-ray powder diffraction data showed that the sample adopt the cubic crystal structure having the space group Pm[overline 3]m. Thermogravimetric analysis of prehydrated samples showed significant mass losses beyond 300C due to loss of protons as water vapor. Scanning electron microscope images show that the grain size of the spark-plasma sintered dense sample was smaller than that of solid-state sintered porous sample. The highest total proton conductivity (210−3 S cm−1 at 450C) was found for dense spark-plasma sintered sample under wet H2 than the samples prepared by other routes.

Oxygen bulk diffusion and surface exchange in Sr-substituted La2NiO4 + δ

Authors Zuoan Li, Reidar Haugsrud and Truls Norby
Source
Solid State Ionics
Volume: 184, Issue: 1, Pages: 42–46
Time of Publication: 2011-03
Abstract The oxygen bulk diffusion and surface exchange in Sr-substituted La2NiO4 + δ were investigated separately in this work. The oxygen flux through La2−xSrxNiO4 + δ (x = 0.1 and 0.2) was measured as a function of temperature and the oxygen self diffusion coefficients, DO, were extracted. The results show that the higher the Sr concentration, the lower the oxygen permeation and the higher the activation energy of DO. The surface exchange rate was determined by measuring isotope exchange with a mass spectrometer. The Sr substitution leads to higher surface exchange rate with lower activation energy. The incorporation of ionized atomic oxygen into surface vacancies was suggested to be the rate determining step.
Keywords Oxygen diffusion; Defect chemistry; Surface exchange; Rate determining step (rds); La2NiO4 + δ; La2−xSrxNiO4 + δ
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Development of an In Situ Surface Deformation and Temperature Measurement Technique for a Solid Oxide Fuel Cell Button Cell

Authors Huang Guo, Gulfam Iqbal, Bruce S. Kang
Source
International Journal of Applied Ceramic Technology
Volume: 7, Issue: 1, January/February, Pages: 55-62
Time of Publication: 2010-01
Abstract A novel experimental technique is developed to measure the in situ surface deformation and temperature of a solid oxide fuel cell (SOFC) anode surface along with the cell electrochemical performance. The experimental setup consists of a NexTech ProboStat™ SOFC button cell test apparatus integrated with a Sagnac interferometric optical method and an infrared sensor for in situ surface deformation and temperature measurements, respectively. The button cell is fed with hydrogen or simulated coal syngas under SOFC operating conditions. The surface deformation is measured over time to estimate the anode structural degradation. The cell surface transient temperature is also monitored with different applied current densities under hydrogen and simulated coal syngas. The experimental results are useful to validate and develop SOFC structural durability and electrochemical models.

Synthesis; Functionalization; and Environmental Stabilization of ZnO Nanobridge Transducers for Gas and Liquid-phase Sensing

Authors A.D. Mason, C.-C. Huang, S. Kondo, M.T. Koesdjojo, Y.H. Tennico, V.T. Remcho and J.F. Conley Jr.
Source
Sensors and Actuators B: Chemical
Volume: 155, Issue: 1, Pages: 245–252
Time of Publication: 2011-07
Abstract Three methods of functionalizing ZnO NW surfaces with biotin were demonstrated. Biotinylated ZnO NWs were found to dissolve during exposure to deionized (DI) water, so a chemical vapor deposition (CVD) process was developed for parylene-A, a common moisture barrier with an amine group which allows further functionalization. Parylene-A coated ZnO NWs were found to be resistant to dissolution. Electrical measurements on parylene-A coated nanobridge devices showed normal operation with higher dark current and an attenuated response to UV and O2, indicating the ability to modulate environmental sensitivity. This work demonstrates the novel use of parylene-A coatings as an encapsulation layer as well as a potential starting platform for general functionalization of ZnO NW devices for selective sensing.
Keywords ZnO; Nanowires; Functionalization; Sensors
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Correlation between microstructure and electrical conductivity in composite electrolytes containing Gd-doped ceria and Gd-doped barium cerate

Authors Mudrika Khandelwal, A. Venkatasubramanian, T.R.S. Prasanna and P. Gopalan
Source
Journal of the European Ceramic Society
Volume: 31, Issue: 4, Pages: 559–568
Time of Publication: 2011-04
Composite; Ceria; Impedance spectroscopy; Electrical conductivity; Fuel cell
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The properties of scandium and cerium stabilized zirconium thin films formed by e-beam technique

Authors Darius Virbukas, Giedrius Laukaitis, Julius Dudonis and Darius Milčius
Source
Solid State Ionics
Volume: 188, Issue: 1, Pages: 46–49
Time of Publication: 2011-04
Abstract Scandium and ceriumstabilizedzirconium (10Sc1CeSZ) thin ceramic films were formed evaporating (ZrO2)0.89(CeO2)0.01(Sc2O3)0.10 micro powder using e-beam evaporation technique. The influence of deposition rate on formedthinfilms electrical properties and microstructure was studied. 10Sc1CeSZ thinfilms were deposited on two types of different substrates: optical quartz (SiO2) and Alloy 600 (Fe–Ni–Cr). Deposition rate was changed from 2 to 16 /s to understand its influence on thinfilm formation and other properties. The formed 10Sc1CeSZ thinfilms keep the cubic crystal structure as the initial evaporated powder material but change the main crystallographic peak from (111) to (200) for both types of substrate and used deposition rates. It was determined that the crystallites size increases from 19.0 to 24.9 nm and from 15.6 to 19.9 nm on optical quartz and Alloy 600 respectively by increasing the deposition rate (in range from 2 to 16 /s). The thinfilm density decreases by increasing the deposition rate. The ionic conductivity of 10Sc1CeSZ thinfilms was determined by impedance spectroscopy in the frequency range from 0.1 Hz to 1.0 MHz in temperature range from 473 K to 873 K. The best ionic conductivity σtot = 4.91 10− 2 Sm− 1 at 873 K temperature and the lowest value of activation energy ΔEa = 0.88 eV were found for 10Sc1CeSZ thinfilmsformed at 4 /s deposition rate.
Keywords Scandium and cerium stabilized zirconium (10Sc1CeSZ); Electron beam deposition; Solid oxide fuel cells (SOFC); Ionic conductivity
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Ethanol internal steam reforming in intermediate temperature solid oxide fuel cell

Authors Stefan Diethelm, Jan Van Herle
Source
Journal of Power Sources
Volume: 196, Issue: 17, Pages: 7355–7362
Time of Publication: 2011-09
Abstract This study investigates the performance of a standard Ni–YSZ anode supported cell under ethanolsteamreforming operating conditions. Therefore, the fuelcell was directly operated with a steam/ethanol mixture (3 to 1 molar). Other gas mixtures were also used for comparison to check the conversion of ethanol and of reformate gases (H2, CO) in the fuelcell. The electrochemical properties of the fuelcell fed with four different fuel compositions were characterized between 710 and 860 C by I–V and EIS measurements at OCV and under polarization. In order to elucidate the limiting processes, impedance spectra obtained with different gas compositions were compared using the derivative of the real part of the impedance with respect of the natural logarithm of the frequency. Results show that internalsteamreforming of ethanol takes place significantly on Ni–YSZ anode only above 760 C. Comparisons of results obtained with reformate gas showed that the electrochemical cell performance is dominated by the conversion of hydrogen. The conversion of CO also occurs either directly or indirectly through the water–gas shift reaction but has a significant impact on the electrochemical performance only above 760 C.
Keywords SOFC; Ni–YSZ anode; Ethanol; Internal reforming; Coking; Impedance spectroscopy
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Synthesis and electrical properties of Gd2MO5 (M = Zr, Hf)

Authors L. P. Lyashenko, L. G. Shcherbakova, D. A. Belov, E. I. Knerel’man and N. N. Dremova
Source
Neorganicheskie Materialy
Volume: Vol. 46, No. 12, Pages: pp. 1476–1482
Time of Publication: 2010-08
Abstract Polycrystalline Gd2ZrO and Gd2HfO5 have been prepared by heat-treating coprecipitated oxide mixtures, and their order-disorder phase transitions have been studied in the range 20–1600C. The materials have been shown to consist of nanostructured grains with a nanodomain size of ∼40 nm. Their electrical conductivity has been determined by impedance spectroscopy in air between 300 and 1000C. The 1000C conductivities of Gd2ZrO5 and Gd2HfO5 are 3.7 10−3 and 1.8 10−3 S/cm, and the respective effective activation energies are 1.37 and 1.56 eV.

Proton Conductivity in Mixed B-Site Doped Perovskite Oxide BaZr0.5In0.25Yb0.25O3−delta

Authors Istaq Ahmed,1,2 Francis G. Kinyanjui,1 Seikh M. H. Rahman,1 Patrick Steegstra,3 Sten G. Eriksson,1 and Elisabet Ahlberg3
Source
J. Electrochem. Soc.
Volume: Volume 157, Issue: Issue 12, Pages: B1819-B182
Time of Publication: 2010-12
Abstract A wet chemical route was used to prepare the oxygen deficient codoped perovskite oxide BaZr0.5In0.25Yb0.25O3−. Analysis of X-ray powder diffraction data showed that the sample belongs to the cubic crystal system with space group Pmm. Dynamic thermogravimetric (TG) analysis confirmed complete filling of oxygen vacancies (V) by protonic defects (OH) during the hydration process. The proton conductivity was investigated by impedance spectroscopy. The bulk and total conductivities of prehydrated BaZr0.5In0.25Yb0.25O3− were found to be 8.510−4 and 2.210−5 S cm−1, respectively, at 300C. The total conductivity in the codoped perovskite oxide was higher compared to that of the respective single doped perovskite oxides with the same doping level. The bulk and grain-boundary mobility and diffusion coefficients of protons were calculated at 200C using impedance and TG data to obtain the conductivity and proton concentration, respectively. The high bulk diffusivity (2.310−7 cm2 s−1) was obtained which indicates that the protons are more free to move in the heavily doped matrix compared to the lightly doped systems where trapping of protons occurs.
Keywords barium compounds, proton exchange membrane fuel cells, thermal analysis, vacancies (crystal), X-ray diffraction, zirconium compounds
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Electrical Conductivity of Nanostructured Fluorite-Like Sc2Ti3O12

Authors L.P. Lyashenko, L.G. Shcherbakova, D.A. Belov, and A.V. Knotko
Source
Inorganic Materials
Volume: 45, Issue: 5, Pages: 543-549
Time of Publication: 2009
Abstract Single-crystal and polycrystalline samples of Sc4Ti3O12 have been shown to contain nanodomains (10–50 nm) with different degrees of ordering, coherent with the fluorite-like matrix. The oxygen-ion conductivity of this compound has been determined in the range 300–1000C in air using impedance spectroscopy. The nanostructured single-crystal and polycrystalline samples are close in the activation energy for bulk conduction at both low and high temperatures: ≃1.26 and 1.29 eV in the range 300–775C, ≃1.98 and 2.07 eV in the range 775–1000C.
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