Oxygen ionic transport in SrFe1?yAlyO3?δ and Sr1?xCaxFe0.5Al0.5O3?δ ceramics |
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| Affiliation: | 1. Department of Ceramics and Glass Engineering, CICECO, University of Aveiro, Aveiro 3810-193, Portugal;2. Institute of Physicochemical Problems, Belarus State University, 14 Leningradskaya Str., Minsk 220050, Belarus;3. Institute of Solid State Chemistry, Ural Division of RAS, 91 Pervomayskaya Str., Ekaterinburg 620219, Russia;1. School of Physics and Materials Science, Thapar University, Patiala, Punjab 147004, India;2. Department of Chemical Engineering, Indian Institute of Technology, Delhi 110016, India;1. Department of Physics, Faculty of Science, Naresuan University, Phitsanulok 65000, Thailand;2. Research Center for Academic Excellence in the Petroleum, Petrochemical and Advanced Material, Faculty of Science, Naresuan University, Phitsanulok 65000, Thailand;3. Center of Excellence in Applied Physics, Faculty of Science, Naresuan University, Phitsanulok 65000, Thailand;1. Department of Environment Engineering, Nanjing Institute of Technology, 211167 Nanjing, China;2. School of Chemical Engineering, Nanjing University of Science & Technology, 210094 Nanjing, China;3. School of Environment Engineering, Nanjing University of Information Science & Technology, 210044 Nanjing, China;1. Institute of Solid State Physics, Russian Academy of Science, Moscow District, 2 Academician Ossipyan str., 142432 Chernogolovka, Russia;2. Georg-August-Universität Göttingen, IV. Physikalisches Institut, Friedrich-Hund-Platz 1, D-37077 Göttingen, Germany;1. University of Newcastle, Callaghan Australia 2308, Discipline of Chemistry;2. CSIRO Energy Technology, 10 Murray Dwyer Circuit, Steel River Industrial Estate, Mayfield West 2304;1. College of Materials Science and Engineering, Fuzhou University, Fuzhou 350116, PR China;2. Quanzhou Arts and Crafts Vocational College, Quanzhou 362500, PR China |
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| Abstract: | The oxygen permeability of mixed-conducting Sr1?xCaxFe1?yAlyO3?δ (x=0–1.0; y=0.3–0.5) ceramics at 850–1000 °C, with an apparent activation energy of 120–206 kJ/mol, is mainly limited by the bulk ionic conduction. When the membrane thickness is 1.0 mm, the oxygen permeation fluxes under pO2 gradient of 0.21/0.021 atm vary from 3.7×10?10 mol s?1 cm?2 to 1.5×10?7 mol s?1 cm?2 at 950 °C. The maximum solubility of Al3+ cations in the perovskite lattice of SrFe1?yAlyO3?δ is approximately 40%, whilst the brownmillerite-type solid solution formation range in Sr1?xCaxFe0.5Al0.5O3?δ system corresponds to x>0.75. The oxygen ionic conductivity of SrFeO3-based perovskites decreases moderately on Al doping, but is 100–300 times higher than that of brownmillerites derived from CaFe0.5Al0.5O2.5+δ. Temperature-activated character and relatively low values of hole mobility in SrFe0.7Al0.3O3?δ, estimated from the total conductivity and Seebeck coefficient data, suggest a small-polaron mechanism of p-type electronic conduction under oxidising conditions. Reducing oxygen partial pressure results in increasing ionic conductivity and in the transition from dominant p- to n-type electronic transport, followed by decomposition. The low-pO2 stability limits of Sr1?xCaxFe1?yAlyO3?δ seem essentially independent of composition, varying between that of LaFeO3?δ and the Fe/Fe1?γO boundary. Thermal expansion coefficients of Sr1?xCaxFe1?yAlyO3?δ ceramics in air are 9×10?6 K?1 to 16×10?6 K?1 at 100–650 °C and 12×10?6 K?1 to 24×10?6 K?1 at 650–950 °C. Doping of SrFe1?yAlyO3?δ with aluminum decreases thermal expansion due to decreasing oxygen nonstoichiometry variations. |
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