Transport Number Of Oxide Ion Research Articles

Conduction mechanism of donor and acceptor doped sodium niobate-based ceramics

Recently, NaNbO3 (NN) has become a hot topic of current research due to its antiferroelectric energy storage properties, which demand that the ceramics withstand large applied electric fields. The breakdown strength is dependent on conduction properties, but there is limited research on the conduction mechanisms of NN. Here we report that A-site donor-doping of Bi3+ (BixNa1-3xNbO3) and B-site acceptor-doping of Mg2+ (NaNb1-2/5yMgyO3) in NN lead to dramatic changes in the magnitude of the bulk conductivity (σb) and the conduction mechanism of NN ceramics. Undoped NN exhibits mixed conduction behavior with an oxide ion transport number (tion) of ∼0.44, and σb of ∼10−6 S/cm at 600 °C. A low level of Bi3+ doping (x = 0.06) suppresses the NN mixed conduction mechanism to electron conduction (tion ∼ 0), and the bulk conductivity increases significantly, σb > 10−4 S/cm at 600 °C. On the other hand, Mg2+ doping (y = 0.06) samples mainly change the σb, with the mixed ion/hole conduction (tion ∼ 0.43) and σb > 10−4 S/cm at 700 °C. The results show that the conductivity of NN increases and exhibits different conduction mechanisms with the doping of Bi3+ and Mg2+. Aliovalent doping is not beneficial to improving the insulation properties. Thus, this work provides theoretical guidance for the study of energy storage characteristics and the suppression of leakage behavior of high-temperature dielectric capacitors.

Anomalous grain boundary conduction in BiScO3-BaTiO3 high temperature dielectrics

A combination of X-ray diffraction, analytical-electron microscopy, differential scanning calorimetry, impedance spectroscopy and electromotive force measurements (for oxide-ion transport number measurements, tion) are used to report on the influence of a small amount of a continuous Bi2O3-rich phase along the grain boundaries in sample composition x = 0.4 (BS0.4BT) of the high temperature dielectric solid solution series, x(BiScO3)-(1-x)(BaTiO3). Its presence produces a dramatic change in conductivity of ~ two orders of magnitude and a switch in tion over the range ~ 600 - 800 °C that is not observed for other ceramics with lower BiScO3 content. Below ~ 700 °C the grain boundaries in BS0.4BT act as electrically blocking layers and dominate the impedance of the ceramics. In contrast, at > 800 °C the grain boundaries become highly conductive due to a polymorphic phase transition to, and melting of δ-Bi2O3 which results in the current percolating along the grain boundaries and therefore avoiding the grains. The value of tion increases from ~ 0.13 at ~ 600 °C to near unity at ~ 800 °C for BS0.4BT, consistent with oxide ion conduction due to the presence of liquid Bi2O3 at grain boundary regions. This behaviour was reproduced by adding a small excess of 3 wt% Bi2O3 into x = 0.3 (BS0.3BT) samples to induce a Bi2O3-rich grain boundary phase, not otherwise present in this composition.

Synthesis and ion transport properties of RE3GaO6 (RE = rare earth) oxide ion conductors

First-principles calculations were conducted, which proposed that members of the RE3GaO6 (RE = rare earth) system were oxide ion conductors. This study experimentally verified oxide ion conduction in Dy3GaO6, Er3GaO6, and Nd3GaO6. The sintered bodies were synthesized by a solid-state reaction method, and their properties were characterized. The samples with dopants were observed to be mixed electron and oxide ion conductors. Dy2.85Ca0.15GaO6-δ exhibited oxide ion conductivities of 2.1 × 10−4 S/cm at 973 K, with an oxide ion transport number of 21 % under O2 gas flow. Additionally, the Rietveld refinement suggested that oxide ion migration might occur via the oxide ion vacancy between the O2 sites. Overall, the oxide ion conductivities of RE3GaO6 increased in the following order: Nd > Dy > Er, which was in good agreement with that predicted by using the first-principles calculations. The discrepancy between the experimentally measured and predicted conductivities was caused by the solid-solution limit at the RE site for the dopants.

Difference in Oxide Ion Conduction Properties of Oxide Ion Excess and Cation Deficient PbWO4s and Oxide Ion Deficient CaWO4

Introduction When lanthanum ions are partly substituted for lead in PbWO4 with sheelite-type structure, high oxide ion conduction appeared at elevated temperature [1]. From the density measurement, it has been reported that oxide ion interstitials are formed for the substitution as Pb1-xLaxWO4+x/2, while Pb1-xLa2/3WO4 shows the defect structure of cation deficiency. While the former system exhibits a little higher oxide ion conduction, both systems show approximately unity of the oxide ion transport number. In recent years, it is also found that CaWO4 with the mineral name of scheelite also exhibit the oxide ion conduction by partly substituting potassium ions for calcium site as Ca1-xKxWO4-x/2. In addition to the electrochemical measurements, we have investigated the high-temperature neutron diffraction on these experiments to clarify the oxide ion conduction paths at high-temperatures. We have reported these results separately and have not compared with concerning defect structure. In the present study, we compare the conduction paths between three types of scheelite-type structured oxide ion conductors from the results of high-temperature neutron diffraction. Experimental Pb1-xLaxWO4+x/2 (x = 0.2), while Pb1-xLa2/3WO4 (x = 0.1) and Ca1-xKxWO4-x/2 (x = 0.2) were prepared by conventional solid-state reaction method started from PbO, La2O3, H2WO4, CaCO3 and K2CO3. The sintering temperatures were selected as 900ºC for PbWO4-based materials and 1000ºC for CaWO4s. The crystalline phase of the obtained samples was confirmed by X-ray diffraction. The sintered samples with the amount of c.a. 10 g are set into a vanadium holder with a thin quartz tube to prevent the reaction of sample with holder, which was mounted to the neutron diffractometer SHRPD in J-PARC. Diffracted neutrons were collected at various temperatures up to 800ºC. Structure analyses were performed by using Z-Rietveld, and the trace of nuclear density was calculated by Z-MEM. BVS calculations were also carried out based on the refined structure data. Results and Discussions Fig. 1 exhibits the nuclear density map of (a) Pb1-xLaxWO4+x/2, (b) Pb1-xLa2/3WO4 and (c) Ca1-xKxWO4-x/2 deduced by maximum entropy method based on the neutron diffraction data collected at 800ºC. For Pb1-xLaxWO4+x/2 with the oxide ion interstitials, nuclear density seems to be distributed to the interstitial site, while the latter two systems without oxide ion interstitials, much less amount of nuclear density is observed at the interstitial sites. Therefore, Pb1-xLaxWO4+x/2 system possess the three-dimensional conduction path allowing higher oxide ion conductivity at elevated temperatures. We will also discuss the conduction path in terms of the bond valence sum.

The influence of excess K2O on the electrical properties of (K,Na)1/2Bi1/2TiO3 ceramics

The solid solution (KxNa0.50-x)Bi0.50TiO3 (KNBT) between Na1/2Bi1/2TiO3 and K1/2Bi1/2TiO3 (KBT) has been extensively researched as a candidate lead-free piezoelectric material because of its relatively high Curie temperature and good piezoelectric properties, especially near the morphotropic phase boundary (MPB) at x ∼ 0.10 (20 mol. % KBT). Here, we show that low levels of excess K2O in the starting compositions, i.e., (Ky+0.03Na0.50-y)Bi0.50TiO3.015 (y-series), can significantly change the conduction mechanism and electrical properties compared to a nominally stoichiometric KNBT series (KxNa0.50-x)Bi0.50TiO3 (x-series). Impedance spectroscopy measurements reveal significantly higher bulk conductivity (σb) values for y ≥ 0.10 samples [activation energy (Ea) ≤ 0.95 eV] compared to the corresponding x-series samples which possess bandgap type electronic conduction (Ea ∼ 1.26–1.85 eV). The largest difference in electrical properties occurs close to the MPB composition (20 mol. % KBT) where y = 0.10 ceramics possess σb (at 300 °C) that is 4 orders of magnitude higher than that of x = 0.10 and the oxide-ion transport number in the former is ∼0.70–0.75 compared to <0.05 in the latter (between 600 and 800 °C). The effect of excess K2O can be rationalised on the basis of the (K + Na):Bi ratio in the starting composition prior to ceramic processing. This demonstrates the electrical properties of KNBT to be sensitive to low levels of A-site nonstoichiometry and indicates that excess K2O in KNBT starting compositions to compensate for volatilisation can lead to undesirable high dielectric loss and leakage currents at elevated temperatures.

Oxide ion conductivity in doped NdBaInO4

Oxide ion conductivity in doped NdBaInO4 with new type oxygen deficient perovskite was studied and it was found that doping Ti to In site is effective for increasing the oxide ion conductivity. Since increasing amount of doped Ti increased the partial electronic conductivity under reducing atmosphere, the optimized amount of Ti doped for In site exists around 20mol%, namely, NdBaIn0.8Ti0.2O4. The estimated transport number of oxide ion in this optimized composition was higher than 0.8 from H2–O2 oxygen concentration cell, however, it is lower than 0.1 from N2–O2 cell because the hole conduction is dominant in high PO2 range. Consequently, although the oxide ion conductivity is around log(σ/Scm−1)=−2.5 at 1173K, this study reveals that Ti doped NdBaInO4 which is unique edge oxygen facing structure, is a new family of oxide ion conductor.

Chemical stability and electrical property of Ba 1.03Ce 0.6Zr 0.2Yb 0.2O 3– α ceramic

Ba 1.03Ce 0.6Zr 0.2Yb 0.2O 3– α ceramic was prepared by solid state reaction. Phase composition, surface and cross-section morphologies of the material were characterized by using X-ray diffractometer (XRD) and scanning electron microscopy (SEM), respectively. Its chemical stability against carbon dioxide and water steam at high temperature was tested. Ionic conduction of the material was investigated by ac impedance spectroscopy and gas concentration cell methods under different gas atmospheres in the temperature range of 500–900 °C. Using the ceramic as solid electrolyte and porous platinum as electrodes, the hydrogen-air fuel cell was constructed, and the cell performance at the temperature from 500 to 900 °C was examined. The results indicated that Ba 1.03Ce 0.6Zr 0.2Yb 0.2O 3– α was a single-phase perovskite-type orthorhombic system, with high density and good chemical stability under carbon dioxide and water steam atmospheres at high temperature. In wet hydrogen, the material was a pure protonic conductor with the protonic transport number of 1 from 500 to 700 °C, a mixed conductor of proton and electron with the protonic transport numbers of 0.945–0.916 from 800 to 900 °C. In wet air, the material was a mixed conductor of proton, oxide ion and electronic hole. The protonic transport numbers were 0.013–0.003, and the oxide ionic transport numbers were 0.346–0.265. Under hydrogen-air fuel cell conditions, the material was a mixed conductor of proton, oxide ion and electron, the ionic transport numbers were 0.945–0.848. The fuel cell could work stably, and at 900 °C, the maximum power output density was 36.5 mW/cm 2.

Ionic Conduction and Application of Ba1.03Ce0.8Tm0.2O3−α Ceramic

Ba1.03Ce0.8Tm0.2O3−α ceramic with orthorhombic perovskite structure was prepared by conventional solid-state reaction. The conductivity and ionic transport number of Ba1.03Ce0.8Tm0.2O3−α were measured by ac impedance spectroscopy and gas concentration cell methods in the temperature range of 500–900°C in wet hydrogen and wet air. Using the ceramic as solid electrolyte and porous platinum as electrodes, the hydrogen-air fuel cell was constructed, and the cell performance was examined at 500–900°C. The results indicate that the specimen is a pure ionic conductor with the ionic transport number of 1 at 500–900°C in wet hydrogen. In wet air, the specimen is a mixed conductor of proton, oxide ion and electron hole. The protonic transport numbers are 0.071–0.018, and the oxide ionic transport numbers are 0.273–0.365. The conductivities of Ba1.03Ce0.8Tm0.2O3−α under wet hydrogen, wet air or fuel cell atmosphere are higher than those of Ba1.03Ce0.8RE0.2O3−α (REY, Eu, Ho) reported previously by us. The fuel cell can work stably. At 900°C, the maximum power output density is 122.7 mW·cm−2, which is higher than that of our previous cell using Ba1.03Ce0.8RE0.2O3−α (REY, Eu, Ho) as electrolyte.

Ionic Conduction and Fuel Cell Performance of Ba0.98Ce0.8Tm0.2O3−α Ceramic

The perovskite-type oxide solid solution Ba0.98Ce0.8Tm0.2O3−α was prepared by high temperature solid-state reaction and its single phase character was confirmed by X-ray diffraction. The conduction property of the sample was investigated by alternating current impedance spectroscopy and gas concentration cell methods under different gases atmospheres in the temperature range of 500–900°C. The performance of the hydrogen-air fuel cell using the sample as solid electrolyte was measured. In wet hydrogen, the sample is a pure protonic conductor with the protonic transport number of 1 in the range of 500–600 °C, a mixed conductor of proton and electron with the protonic transport number of 0.945-0.933 above 600 °C. In wet air, the sample is a mixed conductor of proton, oxide ion, and electronic hole. The protonic transport numbers are 0.010–0.021, and the oxide ionic transport numbers are 0.471-0.382. In hydrogen-air fuel cell, the sample is a mixed conductor of proton, oxide ion and electron, the ionic transport numbers are 0.942-0.885. The fuel cell using Ba0.98Ce0.8Tm0.2O3−α as solid electrolyte can work stably. At 900 °C, the maximum power output density is 110.2 mW/cm2, which is higher than that of our previous cell using BaxCe0.8RE0.2O3−α (x≤1, RE=Y, Eu, Ho) as solid electrolyte.

Intermediate temperature steam electrolysis using LaGaO 3-based electrolyte

Steam electrolysis was studied by using La 0.9Sr 0.1Ga 0.8Mg 0.2O 3 (LSGM) oxide electrolyte and it was found that H 2 formation rate obeys the Faraday's law suggesting that the transport number of oxide ion in LSGM under electrolysis condition is unity. Ni–Fe alloy cathode is highly active to electrolysis of steam, however, insertion of Ni-SDC (1:9) layer between Ni–Fe cathode and LSGM electrolyte is further effective for improving the electrolysis performance of the cell. The current density at 1.8 V was achieved values of 314 and 254 mA/cm 2 at 1073 and 873 K, respectively. The improved current density by Ni-SDC is mainly assigned to a decreased cathodic overpotential. The electrolysis efficiency which ignored the inserted heat energy, was calculated based on the formed H 2 amount and the consumed electric energy, and it is found that the estimated efficiency was higher than 70%.

Chemical Stability and Electrical Property of BaCe0.7Zr0.2Nd0.1O3−α Ceramic

Abstract BaCe0.7Zr0.2Nd0.1O3−α ceramic was prepared by solid state reaction. Phase composition, surface and fracture morphologies of the material were characterized by using XRD and SEM, respectively. Chemical stability against carbon dioxide and water steam at the high temperature was tested. The conductivity and ionic transport number of the material were measured by ac impedance spectroscopy and gas concentration cell methods in the temperature range of 500–900°C in wet hydrogen and wet air, respectively. Using the ceramic as solid electrolyte and porous platinum as electrodes, the hydrogen‐air fuel cell was constructed, and the cell performance at the temperature from 500 to 900°C was examined. The results indicate that BaCe0.7Zr0.2Nd0.1O3−α was a single phase perovskite‐type orthorhombic system, with high density and good chemical stability in carbon dioxide and water steam atmospheres at the high temperature. The conductivity of the material in wet hydrogen and wet air was increased as the temperature rises. In wet hydrogen, the material was a pure protonic conductor with the protonic transport number of 1 from 500 to 600°C, a mixed conductor of proton and electron with the protonic transport number of 0.973–0.955 from 700 to 900°C. In wet air, the material was a mixed conductor of proton, oxide ion and electron hole. The protonic transport numbers were 0.002–0.003, and the oxide ionic transport numbers were 0.124–0.179. The fuel cell could work stably. At 900°C, the maximum short‐circuit current density and power output density were 156 mA·cm−2 and 40 mW·cm−2, respectively.

Steam Electrolysis Using LaGaO3 Based Perovskite Electrolyte for Recovery of Unused Heat Energy

Application of LaGaO3 based electrolyte for steam electrolysis was studied for the useful utilization of unused heat energy from steelmaking process. It was found that the H2 formation rate almost obeys the Faraday's law suggesting unity of oxide ion transport number in LaGaO3 perovskite under an electrolysis condition up to 2.0 V applied potential. Among the examined cathode catalyst, nickel shows the smallest cathodic overpotential and the addition of Fe to Ni is highly effective for increasing the H2 formation rate in the steam electrolysis at 873 K. The highest H2 formation rate is obtained at the composition of Ni : Fe = 9 : 1. Short stack of the steam electrolysis cell consisting of 25 cells in series connection was also studied and the formation rate of H2 was achieved as large as 70 L/min at 1.8 V applied potential. Heat balance was calculated based on the developed stack level. It became clear that the heat source of 223 K level is enough for sustaining cell temperature because of large Joule heat.

Combustion synthesis of doped LaGaO 3 perovskite oxide with Fe

La 0.7Sr 0.3Ga 0.7Mg 0.1Fe 0.2O 3− δ (LSGMF73712) has been proposed as a new substitute for solid electrolyte in SOFC (solid oxide fuel cells). It has several merits, such as lower operating temperature of SOFC, high transport number of oxide ion and higher electronic conductivity. In this study, the doped-lanthanum gallium with Fe was produced by combustion synthesis, and the effect of particle sizes on sintering behaviors of La(Sr)Ga(Mg)FeO 3− δ samples by spark plasma sintering (SPS) was analyzed by comparing with the traditional solid-state reaction method. In the experiments of the combustion synthesis, lanthanum oxide, strontium carbonate, metallic gallium, pure iron, metallic magnesium and sodium perchlorate were mixed uniformly and were ignited at one end of the sample under the argon atmosphere to complete the combustion process without any additional energy. Not only could this method shorten the processing time, but also it could minimize the sintering temperature in the production. As a result, the product showed definite peaks of lanthanum gallium in X-ray diffraction (XRD) patterns and the product could be sintered at a lower temperature 1473 K by SPS method, in comparison to a conventional solid-state reaction method. Moreover, the sintering temperature of the products could further decrease in a lower temperature 1273 K after ball-mill treatment.

Ionic Conduction in Ba0.95Ce0.8Ho0.2O3‐α.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Intermediate Temperature Steam Electrolysis Using Doped Lanthanum Gallate Solid Electrolyte (2) Effects of CeO<sub>2</sub> Interlayer on Activity

Steam electrolysis is attracting much interest method to produce hydrogen and also the new energy recovery process of wasted heat energy. Up to now, Y2O3 stabilized ZrO2 (YSZ) has been used for a solid electrolyte and so the operating temperature is limited down to 1273K. This study is focused on increasing the performance of steam electrolysis by using LaGaO3 based oxide for electrolyte at intermediate temperature of 873 K, which is upper limit of the obtainable wasted heat. It was found that the formation amount of H2 is almost obeyed the Faraday law up to 1.8 V suggesting that the ionic transport number of oxide ion in LaGaO3 was kept to be 1 under the steam electrolysis condition. The electrolyzing current is improved as following order; La0.6Sr0.4CoO3<Sm0.5Sr0.5CoO3<< Ba0.6La0.4CoO3 for anode and Pt<Ni<Ni-Fe for cathode, respectively. Hydrogen production rate higher than 100 μmol ml-1 min-1 at 873 K and 300 mA cm-2 were successfully demonstrated at 1.8 V in this study. Electrolysis reaction under various reaction conditions are also presented. The H2 formation rate increased with increasing total flow rate due to the diffusion resistance.

Ionic Conduction and Fuel Cell Performance of Ba0.97Ce0.8Ho0.2O3 Ceramic

The perovskite-type-oxide solid solution Ba0.97Ce0.8Ho0.2O3 was prepared by high temperature solid-state reaction and its single-phase character was confirmed by X-ray diffraction. The ionic conduction of the sample was investigated using electrical methods at elevated temperatures, and the performance of the hydrogen-air fuel cell using the sample as solid electrolyte was measured, which were compared with those of BaCe0.8Ho0.2O3. In wet hydrogen, BaCe0.8Ho0.2O3 almost exhibits pure protonic conduction at 600-1000 C, and its protonic transport number is 1 at 600-900 C and 0.99 at 1000 C. Similarly, Ba0.97Ce0.8Ho0.2O3 exhibits pure protonic conduction with the protonic transport number of 1 at 600-700 C, but its protonic conduction is slightly lower than that of BaCe0.8Ho0.2O3, and the protonic transport number are 0.99-0.96 at 800-1000 C. In wet air, the two samples both show low protonic and oxide ionic conduction. For Ba0.97Ce0.8Ho0.2O3, the protonic and oxide ionic transport numbers are 0.01-0.11 and 0.30-0.31 respectively, and for BaCe0.8Ho0.2O3, 0.01-0.09 and 0.27-0.33 respectively. Ionic conductivities of Ba0.97Ce0.8Ho0.2O3 are higher than those of BaCe0.8Ho0.2O3 under wet hydrogen and wet air. The performance of the fuel cell using Ba0.97Ce0.8Ho0.2O3 as solid electrolyte is better than that of BaCe0.8Ho0.2O3. At 1000 C, its maximum short-circuit current density and power output density are 465 mA/cm2 and 112 mW/cm2, respectively.

Electric property of mixed conductor BaIn 1− xCo xO 3− δ

We synthesized BaIn 1− x Co x O 3− δ ( x = 0–0.8) with a defective perovskite structure by partly replacing In with Co in Ba 2In 2O 5. Based on XRD measurements, the synthesized compound was found to have cubic perovskite and orthorhombic brownmillerite structures depending on the amount of Co. BaIn 1− x Co x O 3− δ ( x = 0.2 and 0.3) showed high total electrical conductivities without undergoing the structural transformation that the original Ba 2In 2O 5 undergoes. Some of the samples showed both electronic and oxide ionic conductivities. At the same time, the oxide ionic conductivity was comparable with that of Ba 2In 2O 5. For example, the sample with x = 0.1 had a total electrical conductivity of 4.7 × 10 − 1 S cm − 1 and an oxide ion transport number of 0.52 at 850 °C.

High oxide ion conductivity in Fe and Mg doped LaGaO 3 as the electrolyte of solid oxide fuel cells

La(Sr)Ga(Fe,Mg)O 3 exhibited the high oxide ion conductivity and the electrical power generating property of SOFC single cell using La 0.7Sr 0.3Ga 0.7Fe 0.2Mg 0.1O 3-δ (LSGFM) electrolyte was investigated in this study. The transport number of oxide ion is almost 0.8 in LSGFM and so open circuit potential (OCV) is as low as 0.8 V. OCV was strongly affected by anode materials and the highest OCV was achieved on Ni–Fe bimetallic anode. The extremely high power density was achieved by using LSGFM for electrolyte of SOFC. The maximum power densities of the cells can be elevated by coating with oxide ion conductor film at anode side. The maximum power density increased in the following order for coating film: LSGM > SDC > YSZ. The maximum power density of 197 and 100 mW/cm 2 can be achieved at 873 and 773 K, respectively, when LSGM film deposited on the anode side of LSGFM. Therefore, LSGFM can be used as electrolyte of SOFC operating at intermediate temperature.

Properties and Application of Ceramic BaCe0.8Ho0.2O3−α

Ceramic BaCe0.8Ho0.2O3−α with orthorhombic perovskite structure was prepared by conventional solid state reaction, and its conductivity and ionic transport number were measured by ac impedance spectroscopy and gas concentration cell methods in the temperature range of 600–1000 °C in wet hydrogen and wet air, respectively. Using the ceramics as solid electrolyte and porous platinum as electrodes, the hydrogen-air fuel cell was constructed, and the cell performance at temperature from 600–1000 °C was examined. The results indicate that the specimen was a pure protonic conductor with the protonic transport number of 1 at temperature from 600–900 °C in wet hydrogen, a mixed conductor of proton and electron with the protonic transport number of 0.99 at 1000 °C. The electronic conduction could be neglected in this case, thus the total conductivity in wet hydrogen was approximately regarded as protonic conductivity. In wet air, the specimen was a mixed conductor of proton, oxide ion and electron hole. The protonic transport numbers were 0.01–0.09, and the oxide-ionic transport numbers were 0.27–0.32. The oxide ionic conductivity was increased with the increase of temperature, but the protonic conductivity displayed a maximum at 900 °C, due to the combined increase in mobility and depletion of the carriers. The fuel cell could work stably. At 1000 °C, the maximum short-circuit current density and power output density were 346 mA/cm2 and 80 mW/cm2, respectively.

Stabilized δ-Bi2O3 phase in the system Bi2O3–Er2O3–WO3 and its oxide-ion conduction

In the ternary system Bi2O3–Er2O3–WO3, the truly stabilized δ-Bi2O3 type fcc phase has been prepared in a limited solid-solution region. This δ-phase shows good oxide-ion conduction, e.g., (Bi2O3)0.735(Er2O3)0.21(WO3)0.055 at 550 °C, σ=0.05 S cm−1 with the activation energy=0.9 eV and the oxide-ion transport number=0.94. In contrast to “the stabilized δ-phase” reported to date in the binary system Bi2O3–Ln2O3, where Ln is a lanthanoid element including Y, the present δ-phase indicates very little time-dependent degradation of electrical conductivity because of the realization of stabilization, e.g., (Bi2O3)0.705(Er2O3)0.245(WO3)0.05 at 600 °C showing no degradation up to 1100 h. The present δ-phase is thermally stable up to about 1000 °C, since the melting onset temperature is about 1015 °C with negligibly small weight loss <1%.