Transport Number Of Oxide Ion Research Articles

Electrical conductivity of Ba1−xLaxSc1−yZryO3−δ with defective perovskite structure

Ba1−xLaxSc1−yZryO3−δ with perovskite-related structure was synthesized by dopes of La and Zr to Ba-site and Sc-site of Ba2Sc2O5, respectively. The lattice parameters were refined by the Rietveld analysis with space group Pm3m. The total electrical conductivities of Ba1−xLaxSc1−yZryO3−δ measured by DC four-probe method were found to be about 10−2 S·cm−1 at 1000 °C in air and contributed by oxide ion, proton, and hole. The oxide ion transport number of Ba1−xLaxSc1−yZryO3−δ determined by ion blocking method increased with decreasing temperature.

Oxide ion conductivity in La(Sr)Ga(Fe,Mg)O 3 and its application for solid oxide fuel cells

Oxide ion conductivity in La(Sr)Ga(Fe,Mg)O 3 was investigated in this study and it was found that the oxide ion conductivity increased significantly by doping Fe into Ga site. Although the electrical conductivity monotonically increased with increasing amount of Fe, partial electronic conduction became significant. On the other hand, doping Mg for Ga site simultaneously with Fe is useful for keeping high transport number. By doping Fe for Ga site, perovskite oxide with cubic structure seems to be stabilized and the solid solution limit for Sr for La site is expanded. Considering the transport number of oxide ion and the electronic conductivity, the optimum composition for oxide ion conductivity in this system is La 0.7Sr 0.3Ga 0.7Fe 0.2Mg 0.1O 3 − δ (LSGFM73721). By using this oxide for electrolyte, large power density of 200 mW/cm 2 can be achieved at 873 K.

Electronic Conductivity of La‐Doped Ceria Ceramics

Lanthanum‐doped ceria powder with a composition Ce0.8La0.2O1.9 was prepared by heating the oxalate solid solution (Ce0.8La0.2)2(C2O4)3 at 873 K in air. As‐prepared powder was densified to 96%–97% relative density by sintering in air at 1773 K for 4 h. The electronic current of the disk sample was measured in a temperature range from 773 to 1113 K by the direct current polarization method using a Hebb–Wagner ion‐blocking cell. A linear relationship, which was theoretically predicted, was measured between log σe (electronic conductivity) and E (applied voltage) in the applied voltage range of 0.2–1.0 V. The σe was proportional to PO2−1/4.3≈PO2−1/4.6 in the oxygen partial pressure range of 10−2–10−8 Pa, and to PO2−1/6.7≈PO2−1/7.1 in the oxygen partial pressure range of 10−7.5–10−22 Pa. The apparent activation energy of the electronic conduction was 1.87–1.94 eV. The hole conduction was also measured in the Po2 range of 102–105 Pa. The transport number of oxide ion was 0.96–1.00 at 773–1113 K under an oxygen partial pressure of 10−5 Pa.

Behavior of oxygen concentration cells using BiCuVO x oxide-ion conductor

The mixed oxide, Bi 2Cu 0.1V 0.9O 5.35 often abbreviated as BiCuVO x , is known as an oxide-ionic conductor. The applicability of this oxide to a potentiometric oxygen sensor was investigated. Oxygen concentration cells were fabricated by using a disk of this oxide to test the EMF response to changes in oxygen concentration between 10% and 100% at various temperatures between 300 and 700 °C. As a result, the performances of the cells were found to depend very much on the kinds of electrode materials. When attached with Pt electrodes, the cell produced the EMF response fairly good only at 600 °C and above, whereas the oxide-ion transport number was close to unity even at 500 °C as evaluated from the Faraday efficiency of oxygen pumping current. The use of a perovskite-type oxide (La 0.6Sr 0.4Co 0.8Fe 0.2O 3) instead of Pt was found to enable the cell to work at 400 °C and above. Especially excellent performances were observed when the oxide was mixed with BiCuVO x powder prior to being applied on the BiCuVO x disk as the electrodes.

Estimation of theoretical oxygen permeation rate through La(Sr)Ga(Fe)O 3 mixed conductor

Partial electronic and oxide ion conductivity in La 0.7Sr 0.3Ga 0.6Fe 0.4O 3 (LSGF) was investigated in this study by the ion blocking method. It was seen that LSGF stably exhibits the electronic hole conduction over wide oxygen partial pressure. The estimated oxide ion conductivity decreased with decreasing P O2 and this seem to be caused by decreasing amount of V O¨ which is balanced with Fe valence number. The estimated transport number of oxide ion is reasonably agreed with those estimated by oxygen concentration cell. It was found that the theoretical oxygen permeation rate in LSGF is much larger than that of observed value. Therefore, it is expected that the oxygen permeation rate could be improved by increasing activity of surface catalyst.

Oxide ionic and electronic conduction in Ni-doped LaGaO 3-based oxide

Partial electronic conduction in Ni-doped LaGaO 3-based oxide was investigated by using the ion-blocking method. It was seen that the hole and the electronic conduction originated from doped Ni becomes dominant with decreasing temperature and also with increasing Ni content. P O 2 dependences of hole and electronic conduction decrease with increasing Ni content and it becomes almost P O 2 1/12 and P O 2 −1/12, respectively, at 1073 K when 10 mol% Ni is doped to Ga site. The estimated transport number of oxide ion in Ni-doped LaGaO 3 is always higher than 0.95 in P O 2 range from 1 to 10 −21 atm, which is the important P O 2 range for fuel cell application. Therefore, the main charge carrier is still oxide ion in Ni-doped LaGaO 3. Comparing with the partial electronic conduction in Co-doped sample, the electrolyte domain is wider on Ni-doped sample.

Electrical properties of the tungsten-doped Ba 2In 2O 5

Tungsten doping to the indium site in Ba 2In 2O 5 was examined, and the electrical properties of the solid solutions were measured using electric and electrochemical methods. The result of X-ray diffraction (XRD) suggested that Ba 2(In 1− x W x ) 2O 5+3 x (x=0.05, 0.10 and 0.15) had cubic perovskite-type lattice at room temperature. The lattice parameter decreased with increasing x, reflecting the small ionic radius of tungsten. The conductivities of the solid solutions increased with doping. They were close to those of the Ba 2In 2O 5-based perovskites. These results supported that the partial substitution of W for In stabilized the high-temperature phase of perovskite-type Ba 2In 2O 5 down to lower temperature. The transport number of oxide ion in W-doped Ba 2In 2O 5 increased with an increase of temperature. On the other hand, the contribution of the proton to conduction decreased with increasing temperature.

Electronic conductivity measurement of Sm- and La-doped ceria ceramics by Hebb–Wagner method

Samarium- and lanthanum-doped ceria powders with compositions Ce 0.8Sm 0.2O 1.9 (SDC) and Ce 0.8La 0.2O 1.9 (LDC) were prepared by heating the oxalate solid solution (Ce 0.8R 0.2) 2(C 2O 4) 3 (R=Sm, La) at 873 K in air. As-prepared powders were densified to 96.3–97.4% relative density by sintering in air at 1773 K for 4 h. The electronic current of disk sample was measured at 1073 K for SDC and at 1113 K for LDC by direct current polarization method using Hebb–Wagner ion blocking cell. A linear relationship, which was theoretically predicted, was measured between log σ e (electronic conductivity) and E (applied voltage) for both the samples in the applied voltage range of 0.01–1.0 V. The slopes of log σ e–log P O 2 (oxygen partial pressure) plot for both the samples agreed with the theoretically predicted value of −1/4 in the P O 2 range from 10 2 to 10 −5 Pa. In the P O 2 range lower than 10 −7 Pa, the slopes decreased to −1/7, which was close to the theoretical value of −1/6. In a high pressure range from 10 2 to 10 5 Pa, hole conduction with a slope of 1/4 was measured for LDC. The transport number of oxide ion for the SDC and LDC was significantly higher than the previously reported values.

Conductivity dependence on oxygen partial pressure and transport number measurements of La2Mo2O9

AbstractTransport number measurements and impedance spectroscopy in controlled temperature and atmosphere were used to investigate the electrical properties of La2Mo2O9 sintered samples. These samples were prepared from nanocrystalline La2Mo2O9 powders as obtained from a new soft chemistry route involving the polymerisation of acrylamide. By means of the electromotive force method measurements, the sintered compound was found mainly oxygen conductor in the range of 400 °C-800 °C with oxide-ion transport number greater than 0.99. The effect of the oxygen partial pressure on the electrical conductivity of La2Mo2O9 was investigated by impedance spectroscopy from 1 to 10−22 atm, showing a highly stable conduction properties up to 10−17 atm at 800 °C.

Effect of ionic radius on electrical conductivity of doped SmAlO 3 perovskite oxide

Electrical conductivity of SmAlO 3 substituted by Ni, Mg or Zn ions for Al site was measured as a function of temperature. The electrical conductivity of doped SmAl 0.95M 0.05O 3− x (M=Ni, Mg and Zn) was about three to four orders of magnitude larger than that of undoped SmAlO 3 and increased in the order of Ni, Mg and Zn ions. Effect of ionic radius of doped ions on the electrical conductivity of SmAl 0.95M 0.05O 3− x (M=Ni, Mg and Zn) was discussed. It has been found from the oxygen partial pressure dependence of electrical conductivity that SmAl 0.95Zn 0.05O 3− x was a mixed conductor of oxide ion and hole from 973 to 1273 K. Transport number of oxide ion in SmAl 0.95Zn 0.05O 3− x increased with decreasing temperature. Oxide ion conductivity of SmAl 0.95Zn 0.05O 3− x was compared with those for typical oxide ion conductors and was discussed from the point of view of a tolerance factor.

La ( Sr ) Ga ( Fe ) O 3 Perovskite Oxide as a New Mixed Ionic-Electronic Conductor for Oxygen Permeating Membrane

Fe-doped exhibits a high conductivity (∼1 S/cm) and a high oxygen permeation rate. In particular, the highest conductivity and the oxygen permeating rate were attained at (LSGF). Although a surface catalyst is required, oxygen permeation rate from air to Ar was as high as 2.5 cm3 std/min cm2 at 1273 K and 0.3 mm membrane thickness. Oxygen permeation rate from air to Ar increased in the following order, as the surface catalyst. Since the gradient becomes larger, the oxygen permeation rate drastically increased by changing from air-Ar to -air condition. The products were only CO and having a molar ratio ratio) of almost two. Electronic hole conduction was only observed in LSGF polarization measurement and the oxide ion conductivity estimated is as high as at 1073 K. At high the main defect in LSGF is and and at intermediate concentration of is balanced with that of The estimated transport number of oxide ion was ca. 0.6, which is in a good agreement with that estimated by the electromotive force in gas concentration cells. © 2002 The Electrochemical Society. All rights reserved.

Oxide-ion conductivity of the perovskite-type solid-solution system, (Ba 1− x− ySr xLa y) 2In 2O 5+ y

The oxide-ion conductivity and crystal structure of the perovskite-type (Ba 1− x− y Sr x La y ) 2In 2O 5+ y solid-solution system, which was derived from Ba 2In 2O 5 with a brownmillerite-type structure, were investigated as a function of temperature and oxygen partial pressure. The oxide-ion conductivity was discussed from the viewpoint of the unit cell free volume. The oxide-ion transport number approached unity with increasing La content and the ion conductivity increased with the La or Sr content. The oxide-ion conductivity (1073 K) of (Ba 0.3Sr 0.2La 0.5) 2In 2O 5.5 exhibited a maximum value of 0.12 (S/cm), which exceeded that of yttria-stabilized zirconia. It was found that the oxide-ion conductivity of the present system was dominated by both the unit cell free volume and the amount of mobile oxide ion.

Crystal Structure of Pseudorhombohedral InFe1−xTixO3+x/2 (x=2/3)

The structure of pseudorhombohedral-type InFe1−xTixO3−x/2 (x=2/3) was refined by Rietveld profile fitting. The crystal is a commensurate member of a series in a solution range on InFeO3–In2Ti2O7 including incommensurate structures. The structure with the unit cell of a=5.9188(1), b=10.1112(2), and c=6.3896(1) Å, β=108.018(2)°, and a space group P21/a is the alternate stacking of an edge-shared InO6 octahedral layer and an Fe/Ti–O plane along c*. Metal sites on the Fe/Ti–O plane are surrounded by four oxygen atoms on the Fe/Ti–O plane and two axial ones. Electric conductivities of the order 10−4 S/cm were observed for the samples at 1000 K, while the oxide ion transport number is almost zero as no electromotive force was detected by an oxygen concentration cell.

Nonstoichiometric La(2 - x)GeO(5 - delta) monoclinic oxide as a new fast oxide ion conductor.

Oxide ion conductivity in La(2)GeO(5)-based oxide was investigated and it was found that La-deficient La(2)GeO(5) exhibits oxide ion conductivity over a wide range of oxygen partial pressure. The crystal structure of La(2)GeO(5) was estimated to be monoclinic with P2(1)/c space group. Conductivity increased with increasing the amount of La deficiency and the maximum value was attained at x = 0.39 in La(2 - x)GeO(5 - delta). The oxide ion transport number in La(2)GeO(5)-based oxide was estimated to be unity by the electromotive force measurement in H(2)-O(2) and N(2)-O(2) gas concentration cells. At a temperature higher than 1000 K, the oxide ion conductivity of La(1.61)GeO(5 - delta) was almost the same as that of La(0.9)Sr(0.1)Ga(0.8)Mg(0.2)O(3 - delta) or Ce(0.85)Gd(0.15)O(2 - delta), which are well-known fast oxide ion conductors. On the other hand, a change in the activation energy for oxide ion conductivity was observed at 973 K, and at intermediate temperature, the oxide ion conductivity of La(1.61)GeO(5 - delta) became much smaller than that of these well-known fast oxide ion conductors. The change in the activation energy of the oxide ion conductivity seems to be caused by a change in the local oxygen vacancy structure. However, doping a small amount of Sr for La in La(2)GeO(5) was effective to stabilize the high-temperature crystal structure to low temperature. Consequently, doping a small amount of Sr increases the oxide ion conductivity of La(2)GeO(5)-based oxide at low temperature.

Transition Metal D$ LaGaO3 Perovskite Fast Oxide Ion Conductor and Intermediate Temperature Solid Oxide Fuel Cell

ABSTRACTDoping transition metal cation is known to enhance the electric conduction of solid electrolytes, however, the ionic conduction can be improved by doping the small amount of transition metal, in particular, doping Co is effective for improving the oxide ion conductivity. In this investigation, oxide ion conductivity of LaGaO3 based oxide doped with Co were investigated in detail. It was found that LaGaO3 doped with Co for Ga site (LSGMC) show a notable oxide ion conductivity over a wide range of oxygen partial pressures, although a hole conduction was appeared by addition of excess amount of Co. Considering the electrical conductivity and transport number of oxide ion, the optimized composition of LSGMC seems to be existed at La0.8.Sr0.2, Ga0.8,.Mg0.115 CO0.085O3. Power generation characteristics of fuel cells was greatly improved by using LSGMC for electrolyte and extremely large power density can be obtained on both H2- O2 and H2-air cells. In particular, the maximum power density was attained to a value of 1.53 and 0.50 W/cm2 at 1073 and 873 K, respectively, on H2–O2 cell when the thickness of electrolyte was 0.18 mm. Furthermore, almost similar large power density was attained when air was used as oxidant. The high power density of cell demonstrated in this study suggests that the operating temperature of SOFC can be decreased by using LSGMC for electrolyte.

Electric conductivity and crystal structure of neodymium-containing binary rare-earth metal oxide fluorides

Nd 2Ln 2O 3F 6 compounds (Ln; Y-Lu) are prepared by firing the mixture of 1-mol Nd 2O 3 and 2-mol LnF 3 at 1373 K for 2 h in argon. The crystal system of Nd 2Ln 2O 3F 6 can be assigned into pseudo-tetragonal (monoclinic). Nd 2Ln 2O 3F 6 compounds, except Ln: Nd, Yb and Lu, gave a high oxide ion conductivity of more than 1.0 S m −1 at 923 k. Among them, Nd 2Eu 2O 3F 6 gave the highest conductivity of 5.0 S m −1 under an oxygen partial pressure of 0.4 Pa. The oxide ion transport number for Nd 2Ln 2O 3F 6 (Ln: Y, Ce, Sm, Gd) decreases as the temperature falls. On the other hand, Nd 2Eu 2O 3F 6 holds a number of more than 0.9 even at 723 K. As the result of X-ray diffraction Rietveld analysis, the crystal structure of Nd 2Eu 2O 3F 6 was found to be expressed by the monoclinic based on the defect double layered fluorite structure (monoclinic-D″LF). The lattice constants of the monoclinic D″LF structure were calculated to be a 0 = 0.3959 nm, b 0= 1.132 nm, c 0 = 0.5615 nm, β= 134.69 ° and the lattice volume was 0.180 nm 3. The molecular number, Z, was calculated to be 1 from the density data (measured; 6.98 kg m −3, calculated; 6.96 kg m −3). One molecule of Nd 2Eu 2O 3F 6 is in this unit cell. The lattice plane at y = 0.25 crossing vertically with b-axis in the monoclinic-D″LF structure consists of oxide ions and vacant sites formed by defecting of fluoride ion. The oxide ion conduction in Nd 2Eu 2O 3F 6 was supposed to be arising from migration of oxide ion through the defects in the y = 0.25 plane, because the space of the vacant site of fluoride ion is similar to the size of oxide ion.

Polymorphic transformation of δ-Bi 2O 3 stabilized with Ln 2O 3 ( Ln = Sm, Eu, Gd, Tb and Dy) into a new phase with a C-type rare-earth oxide-related structure

This paper describes the polymorphism of the novel phase Bi 1 − x Ln x O 1.5 ( Ln = Sm, Eu, Gd, Tb, and Dy with = 0.38, 0.375, 0.275-0.40, 0.275-0.35, and 0.30−0.35, respectively) which has a C-type rare-earth oxide-related structure. This C-type phase transformed without delay to the δ-Bi 2O 3 type high-temperature phase around 900 °C upon heating. Upon cooling, however, the δ-phase never returned to the original C-type phase. The irreversibility is only apparent, because the δ-phase transformed gradually to the C-type phase by annealing around 800 °C; in other words, the rate of transition from the δ to the C-type phase is extremely sluggish. The electrical conductivity of the C-type phase was not good ( σ = 10 −3.9 S cm −1 at 700 °C), though the oxide-ion transport number was 70% over a temperature range 600 to 850 °C.

Preparation and electrical conductivity of binary rare earth metal fluoride oxides

As new oxide ion conducting solid electrolytes, binary rare earth metal fluoride oxides, Ln a Ln′ b F c O d (Ln and Ln′ are different rare earth elements), were obtained by firing the powder mixtures of rare earth fluorides and oxides at a temperature from 1100–1400°C in an argon atmosphere. Two homogeneous phases were identified to be rhombohedral and tetragonal. The rhombohedral phase was formes as a stoichiometric compound, LnLn′ 2F 3O 3, from an equimolar mixture of LnF 3 and Ln′ 2O 3. The tetragonal one was found to have a wide homogeneity composition of Ln x Ln′ 2(1− x) F 3 x O 3(1− x) where x-value was from 0.58 to 0.78. All of 210 tetragonal compounds ofLn 2Ln′ 2F 6O 3 containing Pr or Nd or both gave a high electrical conductivity more than 10 −2 S cm −1 at 650°C under around 10 −7 atm oxygen and their crystal structures closely resembled the cubic. The charge carrying species of these binary rare earth metal fluoride oxides except Ce and Tb containing compounds was assumed to be the oxide ion. The electrical conductivity of the sintered Nd 2Y 2F 6O 3 sample obtained by hot-pressing at 1250°C under 300 kg cm −2 was measured to be 8.0 × 10 −2 S cm −1 at 650°C, and its oxide ion transport number was calculated to be over 0.93.

Preparation and the electrical conductivity of the binary rare earth metal fluoride oxides

As new oxide ion conducting ceramics, binary rare earth metal fluoride oxides (BMFO, LnLn′F xO y, Ln,Ln′; rare earth) were obtained by firing the powdered mixture of rare earth fluoeide (LnF 3) and oxide (Ln′ 2O 3) at a temperature of 1100–1400 °C in an argon atmosphere. In the solid phase reaction, the anion exchange reaction between LnF 3 and Ln′ 2O 3 took place in the temperature range from 200 to 600 °C to give two simple metal fluoride oxides (SMFO) of LnF xO y and Ln′F xO y, and then above 900 °C, both SMFOs began to react with each other to produce BMFO. Two homogeneous phases were identified to be the rhombohedral and the tetragonal. The rhombohedral phase was formed as a stoichiometric compound (LnLn′ 2F 3O 3) from an equimolar mixture of LnF 3 and Ln′ 2O 3. The tetragonal one was found to have a wide homogeneity composition of Ln xLn′ 2(1−x)F 3xO 3(1−x) where x-value was 0.58–0.78. The electrical conductivity of the tetragonal was at least 100 times higher than for the rhombohedral. All of 210 tetragonal Ln 2Ln′ 2F 6O 3 samples involving reciprocal systems have been investigated. The samples containing Pr or Nd or both gave a high electrical conductivity more than 10 −2 Scm −1 at 650 °C under around 10 −7atm oxygen and their crystal structures closely resembled the cubic. The charge carring species of these BMFOs except Ce and Tb-compounds was assumed to be oxide ion. The electrical conductivity of the sintered Y 2Nd 2F 6O 3 sample obtained by hot-pressing at 1250 °C under 300 kgcm −2 was measured to be 8.0 x 10 −2 Scm −1 at 750 °C, and its oxide ion transport number was calculated to be over 0.93.

Oxide ion and electron mixed conduction in the fluorite-type cubic solid solution in the system Bi2O3-Tb2O3.5

Electrical conduction in sintered oxides of the system Bi2O3-Tb2O3.5 has been investigated. Oxide ion conduction was observed in the rhombohedral (low temperature) phase and the f c c (high temperature) phase present in the composition range less than 20mol% Tb2O3.5. The fcc phase could be stabilized at lower temperatures by adding more than 30 mol % Tb2O3.5. In addition to oxide ion conduction, appreciable electronic conduction appeared in this composition range. The oxide ion transport number of this phase decreased with increasing content of Tb2O3.5 and the specimens having 40–50 mol % Tb2O3.5 showed mixed conduction where electrical conduction was comparably contributed by oxide ions and electrons. Electronic conduction in the fee phase was considered to be due to the change in valence of terbium at high temperatures.