Oxygen ion conductivity in samarium and gadolinium stabilized cerium oxide heterostructures (original) (raw)
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Materials Science, 2015
Sm 0,20 Ce 0,80 O 2 powder was used for the formation of samarium doped cerium oxide (SDC) thin films using e-beam physical vapour deposition. Surface area of powder was 34.9 m 2 /g and particle size-0.3 μm-0.5 μm. Thin films were deposited using physical vapor deposition system on SiO 2 (optical quartz) and Alloy 600 substrates. The deposition rate 0.2 nm/s ÷ 1.6 nm/s and substrate temperature 20 °C ÷ 600 °C were used. Ionic conductivity investigation revealed that the maximum ionic conductivity (1.67 S/m) has the thin film deposited on 300 °C temperature substrate using 0.4 nm/s deposition rate. Minimum ionic conductivity (0.26 S/m) has thin film, which was deposited on 20 °C temperature substrate using 0.8 nm/s deposition rate. Vacancy activation energies vary in 0.87 eV ÷ 0.97 eV range. Furthermore the calculations of crystallite size revealed that crystallite size increases with increasing substrate temperature: from 7.50 nm to 46.23 nm on SiO 2 substrate and from 9.30 nm to 44.62 nm on Alloy 600 substrate. Molar concentration of samarium in initial evaporated material is 19.38 mol % and varies from 11.37 mol % to 21 mol % in formed thin films depending on technological parameters.
Proceedings, 2003
In spite of its undesirable electronic conductivity under reducing atmosphere, a gadolinium doped ceria (CGO) remains one of the most promising candidates for replacing yttria-stabilised zirconia as electrolyte for SOFC, operating at lower temperature. For the first time, atomic layer deposition (ALD), a well-suited method for binary compounds and their doping, was used for the fabrication of SOFC components. CGO thin layers less than 1 pm-thick were achieved by this technique. SEM analysis, EDS measurements, and XRD have been carried out in order to determine the microstructural characteristics of the ALD layers. Dense, uniform, and well-covereing layers have been deposited onto several kinds of substrates, in particular, on porous SOFC electrodes. Furthermore, the electrical properties of CGO thin films were investigated by means of impedance spectroscopy. In particular, the ionic conductivity of the deposited material was determined and compared with the littérature data.
Surface and Coatings Technology, 2007
Ceria and samaria doped ceria thin films were prepared by ion beam assisted electron beam evaporation. Two substrate temperatures were used (200 and 500°C), together with ion assistance, as preparation parameters to obtain thin films with controlled microstructure. The samaria doped ceria films were grown using a multilayer strategy, alternating deposition of ceria and samaria layers. X-ray diffraction and scanning electron microscopy were used to characterise the evolution of the structure and microstructure of the films. The electrical conductivity of the thin films was studied in pure O 2 atmosphere as a function of temperature by two point dc measurements. The transport characteristics of the films (activation energy and conductivity) exhibited clear grain size dependence. The importance of both ionic and electronic contributions to the total conductivity was identified. In particular, the highest electrical conductivity was achieved for ceria samples prepared at 200°C under Ar + assistance. These samples had the smallest grain size (∼ 20 nm). Samaria doped ceria films showed the highest conductivity and activation energies consistent with ionic charge transport when they were prepared at 500°C under Ar + bombardment and doped with 35 wt.% of Sm 2 O 3 .
Solid State Ionics, 2015
Samarium doped cerium oxide (Sm 0.15 Ce 0.85 O 1.925 , SDC) thin films were grown on the Alloy 600 (Fe-Ni-Cr) and optical quartz (SiO 2) substrates using e-beam deposition technique. Formed SDC thin films were characterized using different X-ray diffraction (XRD) techniques, scanning electron microscope (SEM), energy-dispersive spectrometry (EDS) and impedance spectroscopy. The deposition rate of formed SDC thin films was changed from 2 Å/s to 16 Å/s. XRD analysis shows that all thin films have a cubic (FCC) structure and repeat the crystallographic orientation of the initial powders evaporated with different deposition rate and on different substrates. The crystallite size increases from 7.7 nm to 10.3 nm and from 7.2 nm to 9.2 nm on Alloy 600 substrate and optical quartz (SiO 2) substrate respectively as the thin film deposition rate increases. SEM images indicate a dense and homogeneous structure of all formed SDC thin films. The ionic conductivity depends on thin films density and blocking factor. The best ionic conductivity (σ g = 1.34 Sm −1 and σ gb = 2.29 Sm −1 at 873 K temperature, activation energy ΔE g = 0.91 eV and ΔE gb = 0.99 eV) was achieved for SDC thin films formed at 4 Å/s deposition rate. It was found that the highest density (5.25 g/cm 3) and the lowest relaxation time in grain (τ g =9.83 × 10 −7 s), and the lowest blocking factor (0.39) is in SDC thin films formed at 4 Å/s deposition rate. The deposition rate influences the stoichiometry of the formed SDC thin ceramic films.
Journal of the American Ceramic Society, 2009
We demonstrate a modified Hebb-Wagner approach to quantitatively estimate transference numbers for carrier conduction in thin film oxide conductors using blocking electrodes in an inplane geometry. We report ionic transference numbers, t i , for gadolinia-doped ceria (GDC) thin films, a model mixed ionelectron conductor, at 973K and oxygen partial pressure ranging from 0.21 atm down to approximately 10 À22 atm. Our results indicate that GDC reaches the electrolytic regime (t i 5 0.5) at an oxygen partial pressure of 5 Â 10 À19 atm at 973K. This approach may be useful for understanding carrier transport mechanisms in low-dimensional oxide heterostructures with specific relevance to nanostructured energy materials.
Microstructure–electrical conductivity relationships in nanocrystalline ceria thin films
Solid State Ionics, 2002
A study of nanocrystalline oxide thin film processing and influence of microstructure on the electrical properties of nanocrystalline Gd 3 + -doped CeO 2 thin films was reported. Nanocrystalline films on sapphire substrate were prepared using a polymeric precursor spin coating technique. The grain size of these films depends upon the annealing temperatures and the dopant content, where higher content of dopant realized smaller grain size. The electrical conductivity of nanocrystalline Gd 3 +doped CeO 2 thin films was studied as a function of temperature and oxygen activity, and correlated with the grain size. The results show that the electronic conductivity of CeO 2 increases, whereas the ionic conductivity increases in doped samples as the grain size decreases. From these results, the enthalpy of oxygen vacancy formation was determined as a function of grain size. For CeO 2 sample, an enhancement of electronic conductivity was observed with decreasing grain size below 100 nm. In the case of Gd 3 + -doped CeO 2 , the electrical conductivity results show that an increase of the ionic conductivity was observed as the grain size decreased, which is related to a decrease in the activation energy for the ion mobility. D
Ceramics International, 2020
The gadolinium-doped ceria is investigated as electrolyte materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) due to its oxide ion conductivity. The doping of Gd 3+ to Ce 4+ can introduce a small strain in the lattice thereby improved conductivity with low activation energy is expected. The 20 mol. % gadolinium doped ceria (Ce 0.8 Gd 0.2 O 2− δ) nanocrystalline powder is prepared here by citrate-complexation method. The XRD, Rietveld refinement, FTIR, UV-Visible, FESEM/EDX, and a c-impedance techniques are used to characterize this sample. The oxide ion conductivity is determined between 523 − 1023 K. The Ce 0.8 Gd 0.2 O 2− δ shows highest oxide ion conductivity of 6.79 × 10 − 3 S cm − 1 and 1.11 × 10 − 2 S cm − 1 at 973 K and 1023 K, respectively. The Ce 0.8 Gd 0.2 O 2− δ showed lower activation energies of 1.09, 0.70, and 0.88 eV for grain, grain boundary, and total conduction, respectively. Thus, the nano crystalline Ce 0.8 Gd 0.2 O 2− δ is proposed as potential electrolyte for IT-SOFCs.
Mixed Electronic-Ionic Conductivity of Cobalt Doped Cerium Gadolinium Oxide
J Electroceram, 2000
The effect of small amounts (55 mol %) of cobalt oxide on the electrical properties of cerium oxide solid solutions has been evaluated. Ce 0X8 Gd 0X2 O 2Àx (CGO) powder with an average crystallite size of 20 nm served as a model substance for the electrolyte material with a high oxygen ion conductivity and low electronic conductivity in its densi®ed state. Doping the CGO powder by transition metal oxides (MeO) with concentrations below 2 mol % did not change the ionic conductivity nor the electrolytic domain boundary. After long sintering times (2 h) at temperatures above 900 C, MeO and CeO 2 form solid solutions. However, short sintering times or high dopant concentrations lead to an electronic conducting grain boundary phase short circuiting the ionic conductivity of the CGO grains. Choosing proper doping levels, sintering time and temperature allows one to tailor mixed conducting oxides based on CGO. These materials have potential use as electrolytes and/or anodes in solid oxide fuel cells and ion separation membranes.
Electrical characterization of gadolinia doped ceria films grown by pulsed laser deposition
Applied Physics A-materials Science & Processing, 2010
Electrical characterization of 10 mol% gadolinia doped ceria (CGO10) films of different thicknesses prepared on MgO(100) substrates by pulsed laser deposition is presented. Dense, polycrystalline and textured films characterized by fine grains (grain sizes < 18 nm and < 64 nm for a 20-nm and a 435-nm film, respectively) are obtained in the deposition process. Grain growth is observed under thermal cycling between 300 and 800°C, as indicated by X-raybased grain-size analysis. However, the conductivity is insensitive to this microstructural evolution but is found to be dependent on the sample thickness. The conductivity of the nanocrystalline films is lower (7.0 × 10 −4 S/cm for the 20nm film and 3.6 × 10 −3 S/cm for the 435-nm film, both at 500°C) than that of microcrystalline, bulk samples (6 × 10 −3 S/cm at 500°C). The activation energy for the conduction is found to be 0.83 eV for the bulk material, while values of 1.06 and 0.80 eV are obtained for the 20-nm film and the 435-nm film, respectively. The study shows that the ionic conductivity prevails in a broad range of oxygen partial pressures, for example down to about 10 −26 atm at 500°C.