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1.
Abstract In this paper I summarize our recent investigations (Park and Kim, Phys Chem C 111:14903, 2007; Solid State Ionics 179:1329,
2008) on the origin of the grain-boundary resistance in a doped LaGaO 3, a perovskite-structured solid electrolyte. The partial electronic and ionic resistances of the bulk and the grain boundaries,
as well as the total resistance, in 1 mol% Sr-doped LaGaO 3 were measured separately by means of a dc-polarization method and ac-impedance spectroscopy. Both of the partial resistances
at the grain boundaries were greater than the bulk counterparts, indicating that the grain boundaries impede the ionic as
well as the electronic transport in this material. The transference number of the partial electronic conductivity at the grain
boundary was however greater than that in the bulk. This fact strongly suggests that both electronic and ionic charge carriers
deplete at the grain boundaries to form the space-charge zones and that the grain-boundary cores in this material are positively
charged. In light of the fact that the effective charge of the oxygen vacancy (+2) is greater than that of the electron hole
(+1), the oxygen vacancies deplete more sharply in the space-charge zones compared to the electron holes such that the grain
boundaries become more mixed conducting relative to the bulk. These observations verify that the electrical conduction across
the grain-boundaries in 1 mol% Sr-doped LaGaO 3 is governed by the space charge.
Graphical Abstract
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2.
Much attention has been paid to barium zirconates because their high protonic conductivity and chemical stability are excellent
properties for solid electrolytes. However, most studies have focused on highly doped materials such as 10 or 20 mol% Y-doped
barium zirconates. In this study, the bulk and the grain boundary electrical properties of 1 mol% Y-doped barium zirconate
are investigated as a function of temperature, water partial pressure, and oxygen partial pressure. At low temperatures and
in wet atmospheres, the bulk of the barium zirconate predominantly conducts protonic defects, whereas, at high temperatures
and in dry conditions, it is mixed oxygen ionic and electron-hole conducting. In the grain boundary, the protonic conductivity
is a few orders of magnitude lower than the protonic conductivity in the bulk. In this study, possible causes for the low
protonic conduction at the grain boundaries are considered. 相似文献
3.
Electrical conduction in nanostructured 10 mol% Sr- and 15 mol% Mg-doped lanthanum gallate was investigated. The grain boundary conductivity shows mixed ionic and electronic conduction, while the grain conductivity shows ionic conduction. This is attributed to the increase of the contribution of the electron-hole in the grain boundary by the space charge effect. The overall electrical conductivity is governed by the grain boundary conductivity such that nanostructured lanthanum gallate becomes a mixed conductor. 相似文献
4.
Abstract Internal and external interfaces in solids exhibit completely different transport properties compared to the bulk. Transport
parallel to grain or phase boundaries is usually strongly enhanced. Transport perpendicular to an interface is usually blocked,
i.e., transport across an interface is often much slower. Due to the high density of interfaces in modern micro- and nanoscaled
devices, a severe influence on the total transport properties can be expected. In contrast to diffusion in metal grain boundaries,
transport phenomena in boundaries of ionic materials are still less understood. The specific transport properties along metal
grain boundaries are explained by structural factors like packing densities or dislocation densities in the interface region.
In most studies dealing with ionic materials, the interfacial transport properties are merely explained by the influence of
space charge regions. In this study the influence of the interface structure on the interfacial transport properties of ionic
materials is discussed in analogy to metallic materials. A qualitative model based on the density of misfit dislocations and
on interfacial strain is introduced for (untilted and untwisted) phase boundaries. For experimental verification, the interfacial
ionic conductivity of different multilayer systems consisting of stabilised ZrO 2 and an insulating oxide is investigated as a funtion of structural mismatch. As predicted by the model, the interfacial conductivity
increases when the lattice mismatch is increased. 相似文献
5.
Partial oxidation of methane (CH 4 +1/2O 2 CO + 2H 2) is considered as an alternative reforming reaction to steam reforming for production of syngas. This reaction is a slightly exothermic reaction and produces syngas of H 2/CO = 2, which is suitable for the synthesis of hydrocarbon or methanol. In this paper, the catalytic partial oxidation of CH 4 with a membrane reactor using oxygen permeating ceramic, in particular, LaGaO 3-based oxide, is reported. Supported Ni or Rh catalysts are active and selective for this reaction. On the other hand, a mixed ionic and electronic conducting (MIEC) ceramic membrane is useful for obtaining pure oxygen from air when the gradient in oxygen partial pressure is obtained. As for a MIEC membrane, mixed electronic–oxide ionic conductors of Fe- or Co-based perovskite oxides are widely investigated. However, the improvement in stability in a reducing atmosphere is critically required for the MIEC membrane for the application to the membrane reactor for CH 4 partial oxidation. Perovskite oxides of LaGaO 3 doped with Sr for a La site and a Fe, Co, or Ni for a Ga site, respectively, are promising as the oxygen-separating membrane for CH 4 partial oxidation because of high stability in a reducing atmosphere as well as high permeability of oxygen. The partial oxidation of CH 4 with solid oxide fuel cells (SOFCs) is also described. Simultaneous generation of electrical power and syngas is demonstrated by the fabricated fuel cell type reactor using a LaGaO 3-based oxide electrolyte. 相似文献
6.
The overall resistance and resistances of the bulk and grain boundaries of solid electrolyte La 0.8Sr 0.12Ga 0.82Mg 0.18O 2.85 kept for a long time in air at 773-1073 K are studied by impedance spectroscopy. The increase in the electrolyte resistance with time is shown to be connected with that in the resistance of grain boundaries. 相似文献
7.
Abstract Internal and external interfaces in solids exhibit completely different transport properties compared to the bulk. Transport
parallel to grain or phase boundaries is usually strongly enhanced. Transport perpendicular to an interface is usually blocked,
i.e., transport across an interface is often much slower. Due to the high density of interfaces in modern micro- and nanoscaled
devices, a severe influence on the total transport properties can be expected. In contrast to diffusion in metal grain boundaries,
transport phenomena in boundaries of ionic materials are still less understood. The specific transport properties along metal
grain boundaries are explained by structural factors like packing densities or dislocation densities in the interface region.
In most studies dealing with ionic materials, the interfacial transport properties are merely explained by the influence of
space charge regions. In this study the influence of the interface structure on the interfacial transport properties of ionic
materials is discussed in analogy to metallic materials. A qualitative model based on the density of misfit dislocations and
on interfacial strain is introduced for (untilted and untwisted) phase boundaries. For experimental verification, the interfacial
ionic conductivity of different multilayer systems consisting of stabilised ZrO 2 and an insulating oxide is investigated as a funtion of structural mismatch. As predicted by the model, the interfacial conductivity
increases when the lattice mismatch is increased.
Graphical abstract
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8.
Sulfide electrolytes with high ionic conductivities are one of the most highly sought for all-solid-state lithium batteries (ASSLBs). However, the non-negligible electronic conductivities of sulfide electrolytes (≈10 −8 S cm −1) lead to electron smooth transport through the sulfide electrolyte pellets, resulting in Li dendrite directly depositing at the grain boundaries (GBs) and serious self-discharge. Here, a grain-boundary electronic insulation (GBEI) strategy is proposed to block electron transport across the GBs, enabling Li−Li symmetric cells with 30 times longer cycling life and Li−LiCoO 2 full cells with three times lower self-discharging rate than pristine sulfide electrolytes. The Li−LiCoO 2 ASSLBs deliver high capacity retention of 80 % at 650 cycles and stable cycling performance for over 2600 cycles at 0.5 mA cm −2. The innovation of the GBEI strategy provides a new direction to pursue high-performance ASSLBs via tailoring the electronic conductivity. 相似文献
9.
The thick film negative temperature coefficient (NTC) thermistors based on SrFe 0.9Sn 0.1O 3–δ were fabricated on alumina substrate by screen-printed technique. The fired thick films were characterized by X-ray diffraction, scanning electron microscopy and complex impedance analysis. The thick film samples showed compact and homogeneous microstructure. Depending on the thick film composition, the values of the resistivity at 25 °C, thermistor constant and activation energy are in the range of 65.5–4860 Ω cm, 2611–3558 K and 0.229–0.312 eV, respectively. Impedance spectroscopy analysis showed both grain and grain boundary resistances decrease with a rise in temperature for the composition SrFe 0.9Sn 0.1O 3–δ with the glass phases of 5 mol% BaBiO 3 and 5 mol% CuO. The conduction mechanism and relaxation behavior were also discussed. 相似文献
10.
The results of concentration cell electromotive force methods (EMF) and electrochemical impedance spectroscopy measurements on the pyrochlore system Sm1.92Ca0.08Ti2O7–δ are presented. The data have been used to estimate total and partial conductivities and determine transport numbers for protons and oxide ions under various conditions. The EMF techniques employed include corrections for electrode polarisation resistance. The measurements were performed using wet and dry atmospheres in a wide \( {p_{{{{\rm{O}}_{{2}}}}}} \) range using mixtures of H2, N2, O2, and H2O in the temperature region where proton conductivity was expected (500–300 °C). The impedance measurements revealed the conductivity to be mainly ionic under all conditions, with the highest total conductivity measured being 0.045 S/m under wet oxygen at 500 °C. Both bulk and grain boundary conductivity was predominantly ionic, but electronic conductivity appeared to play a slightly larger part in the grain boundaries. EMF data confirmed the conductivity to be mainly ionic, with oxide ions being the major conducting species at 500 °C and protons becoming increasingly important below this temperature. 相似文献
11.
The results of concentration cell electromotive force methods (EMF) and electrochemical impedance spectroscopy measurements on the pyrochlore system Sm 1.92Ca 0.08Ti 2O 7?C?? are presented. The data have been used to estimate total and partial conductivities and determine transport numbers for protons and oxide ions under various conditions. The EMF techniques employed include corrections for electrode polarisation resistance. The measurements were performed using wet and dry atmospheres in a wide $ {p_{{{{\rm{O}}_{{2}}}}}} $ range using mixtures of H 2, N 2, O 2, and H 2O in the temperature region where proton conductivity was expected (500?C300?°C). The impedance measurements revealed the conductivity to be mainly ionic under all conditions, with the highest total conductivity measured being 0.045?S/m under wet oxygen at 500?°C. Both bulk and grain boundary conductivity was predominantly ionic, but electronic conductivity appeared to play a slightly larger part in the grain boundaries. EMF data confirmed the conductivity to be mainly ionic, with oxide ions being the major conducting species at 500?°C and protons becoming increasingly important below this temperature. 相似文献
12.
BiFeO 3 ceramics were sintered in the temperature range of 700–900 °C by using the pure BiFeO 3 powders hydrothermally synthesized at 250 °C. The low reaction temperature and low sintering temperature prevent the element volatilization and phase decomposition. The ceramics sintered at 800 and 850 °C exhibit much dense microstructure with clear grains and grain boundaries. They also show high dielectric constant, dielectric dispersion and low loss tangent. At room temperature, the dielectric behaviors of BiFeO 3 ceramics are mainly attributed to the transition of localized charge carriers and the microstructure of grains and grain boundaries. The temperature dependence of dielectric constant and loss tangent confirms that the localized charge carriers are a main contribution to the dielectric permittivity. Activation energy Eα of relaxation process for the BiFeO 3 ceramic sintered at 850 °C is 0.397 eV. The obtained BiFeO 3 ceramics show magnetic responses, which are relative to the grain size. 相似文献
13.
Abstract The siliceous intergranular phase in acceptor-doped zirconia and ceria and its effect on the ionic conduction across the grain
boundaries were reviewed. Not only the abundant siliceous intergranular liquid phase, but also the monolayer-level siliceous
intergranular segregation significantly deteriorates the grain-boundary conduction. To decrease the harmful effect of the
resistive siliceous phase at the grain boundary, ‘additive scavenging’ or ‘precursor scavenging’ can be employed. The former
involves the addition of a secondary phase or another acceptor material with a very high chemical affinity for the siliceous
phase, while the latter involves the intergranular phase changing from having a continuous (blocking) configuration to having
a discrete (non-blocking) configuration. The mechanisms of various scavenging reactions have been explained, compared, and
discussed. 相似文献
14.
Bi 2Al 4O 9 ceramics are difficult to sinter to greater than 80% theoretical density due to peritectic decomposition at 1,070 °C. A novel processing method is discussed where a high-bismuth oxide-based liquid is used as a sintering aid. After sintering, the high bismuth oxide phase is removed by leaching with 40% acetic acid. The resulting samples are phase pure and ∼91% dense. The grain size varies in a wide range with the average grain size of ∼1 μm. The electrical properties of these ceramics were measured as functions of temperature (550–850 °C) and oxygen partial pressure (6×10 −6–1 atm). The total conductivity was separated into electronic and ionic contributions. The low ionic conductivity indicates that the material is not an ‘intrinsically defective fast ion conductor’. The ionic conductivity is due almost exclusively to compensating oxygen vacancies related to impurities. With increasing temperature and decreasing oxygen partial pressure, the electronic conduction dominates over the ionic conduction. 相似文献
15.
Organic ionic plastic crystal (OIPC) electrolytes are among the key enabling materials for solid-state and higher than ambient
temperature lithium batteries. This work overviews some of the parameter studies on the Li|OIPC interface using lithium symmetrical
cells as well as the optimisation and performance of Li|OIPC|LiFePO 4 cells. The effects of temperature and electrolyte thickness on the cycle performance of the lithium symmetrical cell, particularly
with respect to the interfacial and bulk resistances, are demonstrated. Whilst temperature change substantially alters both
the interfacial and bulk resistance, changing the electrolyte thickness predominantly changes the bulk resistance only. In
addition, an upper limit of the current density is demonstrated, above which irreversible processes related to electrolyte
decomposition take place. Here, we demonstrate an excellent discharge capacity attained on LiFePO 4|10 mol% LiNTf 2-doped [C 2mpyr][NTf 2]|Li cell, reaching 126 mAh g -1 at 50 °C (when the electrolyte is in its solid form) and 153 mAh g -1 at 80 °C (when the electrolyte is in its liquid form). Most remarkably, at high temperature operation, the capacity retention
at long cycles and high current is excellent with only a slight (3%) drop in discharge capacity upon increasing the current
from 0.2 C to 0.5 C. These results highlight the real prospects for developing a lithium battery with high temperature performance
that easily surpasses that achievable with even the best contemporary lithium-ion technology. 相似文献
16.
In this work, samples of Y 0.07Sr 0.93Ti 1-xFe xO 3-δ with 20, 40, 60 and 80 mol% of iron amount were prepared by a low-temperature polymer precursor method. The SEM-EDS analysis proved that analyzed Y 0.07Sr 0.93Ti 1-xFe xO 3-δ samples were composites of two Ti- and Fe-rich perovskite samples. This kind of composite consists of two phases in which one has a good ionic and the other electronic conductivity, which makes such a composite a potential mixed ionic and electronic conductors (MIECs) material. The total electrical conductivities of analyzed samples were measured in air atmosphere (cathode conditions in Solid Oxide Fuel Cell). The values changed from ∼10 −3 to 10 −1 S cm −1 and depended on the ratio between two observed perovskite phases. The 0.12 S cm −1 conductivity value at 800 °C for sample with the highest amount of Fe-rich perovskite in the structure makes this composite material a candidate for air electrode in electrochemical devices. 相似文献
17.
Electrical conduction of the oxide BaZr 0.9Y 0.1O 3 − δ is studied by electrochemical impedance spectroscopy as a function of temperature (300–600°C) and the oxygen partial pressure
in gas phase saturated with H 2O or D 2O vapor. The full electrical conduction is separated into components, in particular, the bulk and grain boundary conduction.
It is shown that at P
O2> 1 Pa the BaZr 0.9Y 0.1O 3 − δ conduction is contributed significantly by electron holes whose transference number in air atmosphere may be as high as 0.5–0.6.
In reductive conditions, the electrical transfer involves proton (deuteron) charge carriers. Isotopic effect H/D in the conduction
in the bulk and along the grain boundaries is determined. Isotopic effect H/D in the hole conduction is also revealed. It
is shown that this effect comes out of different solubility of deuterons and protons in the oxide (the thermodynamic isotopic
effect). 相似文献
18.
An oxygen-permeable composite constituted to oxide ionic conductor phase (Ce 0.75Nd 0.25O 1.875) and oxide electronic conductor phase (Nd 1.8Ce 0.2CuO 4) was prepared using the acetate pyrolysis method. Based on electrical conductivity measurements, total electrical conductivity
of 75 mol% Ce 0.75Nd 0.25O 1.875–25 mol% Nd 1.8Ce 0.2CuO 4 composite material was governed by the electronic conduction paths. With respect to the oxygen permeation properties, the
results showed that oxygen permeation properties were unexplainable by a simple composite rule using the electrical transport
properties of the bulk Ce 0.75Nd 0.25O 1.875 and the bulk Nd 1.8Ce 0.2CuO 4. 相似文献
19.
Cathodic reduction of organic semiconductors (charge-transfer complexes and radical-ion salts) at interfaces in Na(Hg)/β-Al 2O 3/organic semiconductor systems is studied by inversion voltammetry and chronopotentiometry. Formation of transition layer
at the organic semiconductor/solid electrolyte interface is revealed. The mechanism of the charge transfer complex and radical-ion
salt cathodic reduction depends on the potential scan rate; the cathodic process at nonmetal electrodes occurs under the conditions
of double injection of electronic and ionic charge carriers to electrode bulk. 相似文献
20.
The interaction of selected point defects and the Σ3(1 1 1)[1 −1 0] symmetrical twin boundary in SrTiO 3 is investigated by density-functional band-structure calculations. The pristine boundary is SrO 3-terminated and exhibits electronic properties which are comparable with the pure bulk phase. Both the mirror-symmetric twin and some laterally shifted structures have low grain boundary energies, thus they may coexist in a real crystal if external stress is applied. With varying chemical potential of the electrons, the TiO 3 sublattice of the pristine boundary is destabilised by both electron enrichment and electron depletion. These results may explain, why different translation states can be observed by electron microscopy within the same bicrystal.Substitutional doping of the Ti columns next to the boundary plane with formally 3+ cations yields a contraction compared with the pure boundary. The same result, accompanied by more pronounced local geometry changes, is obtained for the translation state in the presence of O vacancies. Neutral O vacancies in the boundary plane are the most stable species followed by positively charged O vacancies in the neighbouring Sr/O plane parallel to the boundary. The Fermi level is shifted either upward to metal-derived states by substitutional doping or downward into the O-2p manifold for O vacancies. These findings may rationalise both the observed low, mainly electronic, grain boundary conductivity of SrTiO 3 boundaries and the changes in local potential found at the grain boundary by tunnelling and force microscopy experiments. 相似文献
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