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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.

Hydrogen sensitivity of doped CuO/ZnO heterocontact sensors

Author Seymen Aygn and David Cann
Source
Sensors and Actuators B: Chemical
Volume: 106, Issue: 2, Pages: 837-842
Time of Publication: 2005
Abstract Heterocontact sensors based on p-type CuO and n-type ZnO ceramics have been shown to exhibit a high sensitivity to reducing gas species and an intrinsic selectivity. In this work, doped heterocontact sensors were prepared via solid state synthesis routes. CuO was doped with various monovalent (Li, Na) and isovalent (Ca, Sr, Ni) dopants at different compositions to form both single phase and two phase samples. Effects of dopants on hydrogen sensitivity through conductivity and heterogeneous microstructure were investigated using dc current–voltage measurements and ac impedance analysis. It was observed that both monovalent and divalent dopants increased the hydrogen sensitivity significantly. The highest sensitivity was observed in a 2.5 mol% Ni-CuO/ZnO heterocontact and low amounts of Li doping were shown to greatly enhance the rectifying characteristics.
Keywords Hydrogen sensor; Heterocontact; CuO; ZnO

Synthesis, densification and electrical properties of strontium cerate ceramics

Authors Paul Inge Dahl, 1, Reidar Haugsrud, Hilde Lea Lein, Tor Grande, Truls Norby and Mari-Ann Einarsrud
Source
Journal of the European Ceramic Society
Volume: 27, Issue: 16, Pages: 4461-4471
Time of Publication: 2007

Stability and conductivity study of the BaCe0.9−xZrxY0.1O2.95 systems

Author Zhimin Zhong
Source
Solid State Ionics
Volume: 178, Issue: 3-4, Pages: 213-220
Time of Publication: 2007

Defects and transport properties in Ln6WO12 (Ln = La, Nd, Gd, Er)

Author Reidar Haugsrud
Source
Solid State Ionics
Volume: 178, Issue: 7-10, Pages: 555-560
Time of Publication: 2007

Phase transitions and ferroelectric properties in BiScO3-Bi(Zn1/2Ti1/2)O3-BaTiO3 solid solutions

Authors Chien-Chih Huang, David P. Cann, Xiaoli Tan, and Naratip Vittayakorn
Source
Journal of Applied Physics
Volume: 102, Issue: 4, Pages: 044103
Time of Publication: 2007

Shrinkage Effects of the Conduction Zone in the Electrical Properties of Metal Oxide Nanocrystals: The Basis for Room Temperature Conductometric Gas Sensor

Authors M. Manzanares, T. Andreu, J. D. Prades, J. Arbiol, F. Hernandez-Ramrez, A. Cirera and J. R. Morante
Source
Journal of Sensors
Volume: 2009, Pages: 1-7, doi:10.1155/2009/783675
Time of Publication: 2009

Preparation, electrical and thermal properties of new exfoliated graphite-based composites

Authors I.М. Afanasov, V.А. Morozov, A.V. Kepman, S.G. Ionov, A.N. Seleznev, G. Van Tendeloo and V.V. Avdeev
Source
Carbon
Volume: 47, Issue: 1, Pages: 263-270
Time of Publication: 2009

Structure, defect chemistry, and proton conductivity in nominally Sr-doped Ba3La(PO4)3

Authors N. Sharova, H. Fjellvg, T. Norby
Source
Solid State Ionics
Volume: 180, Issue: 4-5, Pages: 338-342
Time of Publication: 2009

Local structure and ionic conductivity in the Zr2Y2O7–Y3NbO7 system

Authors Stefan T Norberg, Istaq Ahmed, Stephen Hull, Dario Marrocchelli and Paul A Madden
Source
Journal of Physics: Condensed Matter
Volume: 21, Issue: 21, Pages: 215401
Time of Publication: 2009

Thin film chemical sensors based on p-CuO/n-ZnO heterocontacts

Authors C.S. Dandeneau, Y.H. Jeon, C.T. Shelton, T.K. Plant, D.P. Cann and B.J. Gibbons
Source
Thin Solid Films
Volume: 517, Issue: 15, Pages: 4448-4454
Time of Publication: 2009

Phase formation, microstructure, and dielectric properties of (1 − x)PZT–(x)PCN ceramics

Authors A. Prasatkhetragarn, P. Ketsuwan, S. Ananta, R. Yimnirun and D.P. Cann
Source
Materials Letters
Volume: 63, Issue: 15, Pages: 1281-1284
Time of Publication: 2009

Characterization of porous lanthanum strontium manganite (LSM) and development of yttria stabilized zirconia (YSZ) coating

Authors A.K. Sahu, A. Ghosh and A.K. Suri
Source
Ceramics International
Volume: 35, Issue: 6, Pages: 2493-2497
Time of Publication: 2009
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