Investigation of conductivity of (CexY0.2 − x)Sc0.6Zr3.2O8 − δ (0 < x < 0.2) system and its dependence upon oxygen partial pressure (original) (raw)
Related papers
Journal of Alloys and Compounds, 2013
Attempts have been made to synthesize a few compositions in the system Ce 0.90 Mg 0.10Àx Sr x O 1.90 (x = 0.00, 0.02, 0.04 and 0.06) by citrate-nitrate auto-combustion method. XRD patterns reveal that all the samples have fluorite crystal structure similar to ceria. Microstructures of samples have been studied by scanning electron microscope. Ionic conductivity of singly doped and co-doped ceria has been investigated as a function of temperature by AC impedance spectroscopy in the temperature range 200-700°C. Impedance plots show a significant decrease in grain boundary resistance after partial substitution of Sr in Mg-doped ceria in the intermediate temperature range. Composition with x = 0.04 shows the highest ionic conductivity (2.0 Â 10 À2 S/cm at 700°C) among all the samples studied. Ó 2013 Elsevier B.V. All rights reserved. 2 (x = 0.30) system which was synthesized by glycine-nitrate process and they found single phase formation in this system and the grain growth of sintered samples was observed to hindered with an increase in Gd content. Composition Ce 0.90 Gd 0.10 O 1.95 was synthesized using combustion technique by Jadhav et al. [14] and they found that the relative density of the sample was more than 90% at 1200°C which was also confirmed by SEM analysis. The grain and grain boundary conductivity of a GDC (Ce 0.90 Gd 0.10 O 1.95
Effect of Submicron Grains on Ionic Conductivity of Nanocrystalline Doped Ceria
2010
Doped ceria has been considered for high oxygen ion conductivity for solid oxide fuel cells. In the present study, 20 mole% samarium doped nano ceria powder was prepared by wet chemical synthesis and sintered at different temperatures to retain submicron grains (>92-96% density). Ionic conductivity of the sintered pellets was measured using impedance spectroscopy as a function of temperature (200-800 C). The total maximum conductivity was 1 0 × 10 −2 S.cm −1 (at 600 C) for samples sintered at 1200 C. The activation energy at higher test temperature decreases with the decrease in the sintering temperature (by 25%). The grain boundary, grain interior conductivity and activation energy of the electrolyte were correlated to the resulting microstructure. It has been demonstrated that use of doped nano ceria powder as precursor not only reduced the sintering temperature but also provided segregation free grain boundary for engineering higher conductivity dense electrolytes.
Research Journal of Chemistry and Environment, 2021
The search for new cost-effective electrolyte materials for IT-SOFC towards its mass scale commercialization has gained momentum in recent years. The Ca-doped ceria having composition Ce0.91Ca0.09O2 was prepared using the facile conventional solid-state method. The structural and electrical properties of low sintered ceramic samples have been characterized by X-ray diffraction (XRD), UV-VIS diffuse reflectance spectroscopy (DRS) and A.C. impedance technique respectively. The oxide ion conductivity was measured between the temperatures 573 K−973 K in air. The obtained results showed that total conductivity is mainly dependent on the grain boundary effect. The nanocrystalline Ce0.91Ca0.09O2 exhibited the high total ionic conductivity of 7.36 10 3 S cm 1 at 973 K with a lower activation energy of 0.96 eV. The obtained results highlight the use of cost-effective dopant in ceria lattice to develop commercially viable electrolyte materials for IT-SOFC.
Ionics, 2014
Co-doped samples of Ce 0.95−x Ca 0.05 Sr x O 1.95−x , where (x=0.00, 0.01, 0.02, and 0.03), have been prepared by auto-combustion method and characterized to explore their use as a solid electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs). Crystal structure, microstructure, and ionic conductivity have been characterized by X-ray diffraction, scanning electron microscopy, and impedance spectroscopy, respectively. All the compositions have been found to be single phase. Results show that the samples co-doped with Ca and Sr exhibit higher ionic conductivity than the samples singly doped with Ca in the intermediate temperature range. Ce 0.93 Ca 0.05 Sr 0.02 O 2−δ exhibits maximum conductivity among all the compositions. This may be a potential candidate as a solid electrolyte for IT-SOFCs. Keywords Doped ceria electrolyte. Co-doping effect. Ionic conductivity. Solid oxide fuel cells distributed heat-power co-generation, an operation temperature in the range 500-700°C is highly desirable. This is in view of the cost effectiveness because inexpensive stainless steel may be used for this purpose. Doped ceria electrolytes have attracted great interest in recent years because of their potential as a solid electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs) application [7]. In CeO 2 , temperature facilitates movement of oxygen ions through oxygen vacancies which are produced in the oxygen sublattice to neutralize the deficiency of charge created by lower valent dopant cations. Doped ceria oxides show much higher ionic conductivity at relatively low temperatures (500-700°C) as compared with yttria-stabilized zirconia. These have been extensively studied as the most promising electrolyte materials for IT-SOFCs. Among the various ceria compositions investigated so far [8-19], Gdand Sm-doped ceria (GDC and SDC) are considered as the most suitable low-temperature solid electrolytes for IT-SOFCs application. Both Gd 2 O 3 and Sm 2 O 3 , however, are very costly. Therefore, there is an increasing interest to develop new cost-effective ceria-based electrolytes. Ceria doped with alkaline earth oxides such as CaO [20, 21] and SrO [22, 23] has been studied extensively. Electrical conductivity of CaO-and SrO-doped ceria is much higher than that of undoped ceria. The highest conductivity was found in the composition Ce 0.90 Ca 0.10 O 1.90 by Shing et al. [24] which is ∼10 −3 S cm −1 at 600°C. Yamashita et al. [25] found that the composition Ce 0.90 Ca 0.10 O 1.90 has the highest conductivity which is ∼10 −2 S cm −1 at 600°C. Banerjee et al. [26] studied the electrical properties of Ce 1−x Ca x O 2−δ (0.05≤x≤0.20) samples prepared by a mixed fuel process followed by sintering at 1,250°C. They found that the composition Ce 0.80 Ca 0.20 O 1.80 exhibits the highest conductivity (1.29×10 −2 S cm −1) at 600°C. Compositions Ce 1−x Ca x O 2−δ with 0.05≤x≤0.20 have been prepared by auto-combustion method and characterized.
Solid state sciences, 2004
Ceria-based solid solutions, especially Gd-doped CeO 2 , have widely been used as electrolytes for use in intermediate-temperature fuel cells. In this study, three groups of Ce 1−x Gd x O 2−δ (0.05 x 0.3) ceramics, with SiO 2 contents of 30, 200 and 3000 ppm, were prepared. This investigation was intended to demonstrate the effects of both gadolinia and silica contents on the ionic conductivities (especially the grain-boundary (GB) contribution). It was found that, with increasing SiO 2 content, the composition of maximum total conductivity shifted to high x values. For example, the composition of maximum total conductivity for the 30 ppm SiO 2 group was x = 0.15. It shifted to x = 0.2 and 0.25 as SiO 2 level increased to 200 and 3000 ppm, respectively. Meanwhile, the values of the maximum total conductivity were reduced significantly with increasing SiO 2 content. Although the three groups showed a similar variation trend in the GB conduction with increasing Gd content, the mechanisms governing this variation trend were different, depending on the SiO 2 content and the Gd content. The composition having the maximum GB conductivity (or the minimum activation energy for the GB conduction) could be taken as a critical value (x C ). Below this value (x C ), the GB conductivity was dominated by space-charge layers or/and resistive siliceous films, which was dependent on the SiO 2 content; and above this value (x C ), the GB conductivity was determined by the segregation of undissolved Gd 2 O 3 at the grain boundaries, which was irrespective of SiO 2 content. 2004 Elsevier SAS. All rights reserved.
Aging behavior and ionic conductivity of ceria-based ceramics: a comparative study
Solid State Ionics, 2004
An understanding of high-temperature aging effects on the electrical properties of electrolytes is very important in selecting optimum compositions for practical applications. The aging behavior and mechanisms of doped zirconia ceramics have been extensively studied. However, little information is available regarding the aging behavior of ceria-based electrolytes. The present study has demonstrated that a high-temperature aging at 1000 jC has a significant effect on the ionic conductivity of the Y-or Gd-doped ceria (Ce 1 À x Y x O 2 À d and Ce 1 À x Gd x O 2 À d ), especially in the case of the Gd doping. The aging behavior is characterized by a critical dopant concentration, above which the aging has a detrimental effect on the conductivity of the doped ceria ceramics. The aging behavior in the doped ceria cannot be explained using the aging mechanisms applied to the doped zirconia. Instead, the formation of the microdomains in the doped ceria has been acknowledged to be the main contribution to the aging behavior of the Y-or Gd-doped ceria ceramics. The formation ability of microdomains has been estimated to be in the order of La 3 + >Gd 3 + >Y 3 + , based on the degree of size mismatch between the dopant ion and Ce 4 + ion. The critical dopant concentrations at which the microdomains start to form for La 3 + , Gd 3 + and Y 3 + in the doped ceria ceramics are x = f 0.15, f 0.2 and f 0.25, respectively. This critical dopant concentration is also an important indication: below which the conductivity is governed by only the association enthalpy, and above which the conductivity is dominated mainly by the microdomains rather than the association enthalpy. D
We study ionic conductivity of heavily doped ceria, doping level close to 50 mol% with multiple lanthanides in the temperature range of 200°C–500°C. The doped ceria is found to be single fluorite phase, where unit cell is dilated to 0.5527 nm, com- pared with pure ceria (0.5422 nm). Electrical characterization by impedance spectroscopy reveals that sample sintered at lower temperature (1400°C) has consistently higher bulk con- ductivity compared to sample sintered at higher (1600°C) tem- perature, throughout the temperature range studied. Activation energy for oxygen vacancy diffusion is close to 1 eV, indicating lesser association of defects with the dopants compared with other heavily doped ceria reported in literature (activation energy ~1.4 eV). The best ionic conductivity is found to be 1.58 3 103 S/cm at 500°C, which is much higher compared with heavily doped ceria reported in literature.
Structural and Ionic Conductivity Studies of Doped Ceria Electrolyte
Electrochemical and Solid-State Letters, 2012
The present study reports synthesis, XRD, Impedance spectroscopy and ionic conductivity of Ce 1−x (Gd 0.5 Pr 0.5) x O 2 (x = 0-0.24) system. These samples were synthesized through the sol-gel process followed by low temperature combustion. The samples were sintered at 1300 • C to obtain dense ceramics (over 98%). XRD confirms the single phase with a cubic structure. The two-probe a.c. impedance spectroscopy was used to study the ionic conductivity of doped ceria samples. The Ce 0.88 (Gd 0.5 Pr 0.5) 0.12 O 2 , Ce 0.84 (Gd 0.5 Pr 0.5) 0.16 O 2 compositions showed highest grain ionic conductivity values i.e., 1.012 × 10 −2 S/cm and 1.059 × 10 −2 S/cm respectively at 500 • C.
Electrical conductivity of undoped, singly doped, and co-doped ceria
Ionics, 2011
In order to investigate the effect of single doping and co-doping on the enhancement of ionic conductivity in ceria (CeO 2), CeO 2 and a few compositions in the system Ce 0.85 Sm 0.15−x Gd x O 1.925 (x=0.00, 0.06, 0.09, and 0.15) were prepared using citrate-nitrate auto-combustion method. Gels were characterized by simultaneous differential thermal analysis and thermogravimetric analysis to confirm the formation of end product from the precursor. All the compositions were found to be single-phase solid solution from their X-ray diffraction pattern. Complex plane impedance analysis clearly revealed the contribution of grains, grain boundaries, and electrode specimen interface to the total value of the resistance. The value of activation energy, E a , of conduction shows that the conduction process is mainly due to diffusion of O 2− ions through oxygen vacancies. Effect of doping has been analyzed using the concept of radius mismatch and effective index reported earlier in the literature.
Mixed conductivity, thermal expansion, and oxygen permeability of Ce(Pr,Zr)O
Solid State Ionics, 2005
The use of Pr x Ce 1 À x O 2 À d fluorites in electrochemical devices is hindered by several fundamental problems, one of which is the high thermal expansion coefficients (TECs), which have been shown to vary in the range (10 -40) Â 10 À 6 K À 1 between the temperatures 0 and 1000 -C. Thermogravimetric study shows that such a fluctuation of TECs, and non-linear lattice expansion on heating, are related to oxygen losses and can be controlled, to a substantial extent, by compositional selection. The influence of composition upon resultant mixed conductivity and oxygen permeability values is analysed for the compositions Zr 0.1 Ce 0.9 À x Pr x O 2 À d and