کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
7744530 | 1498227 | 2018 | 9 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
Synthesis and characterization of the novel K2NiF4-type oxide Pr2Ni0.9Co0.1O4 + δ
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کلمات کلیدی
موضوعات مرتبط
مهندسی و علوم پایه
شیمی
الکتروشیمی
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چکیده انگلیسی
Pr2Ni0.9Co0.1O4 + δ (PNCO) powder was synthesized via a freeze drying process by mixing and shock freezing of aqueous metal acetate solutions, vacuum freeze drying of the resulting precursor and thermal treatment to obtain the complex oxide. X-ray powder diffraction and Rietveld refinement confirmed that the material was mainly single phase (< 1 wt% Pr6O11 as secondary phase) with an orthorhombic K2NiF4-type unit cell at room temperature. Precision thermogravimetry between 30 °C and 900 °C showed an irreversible mass increase at T â¥Â 750 °C and pO2 = 0.2 bar which indicated the transition to a higher order Ruddlesden-Popper phase Pr4(Ni,Co)3O10 â x and PrOy. Differential scanning calorimetry in pure Ar and 20% O2/Ar showed a structural phase transition from the orthorhombic to a tetragonal modification at approximately 440 °C. Thermal expansion measurements between 30 °C and 1000 °C at different oxygen partial pressures (1 Ã 10â 3 â¤Â pO2/bar â¤Â 1) indicated two different regions, corresponding to the orthorhombic low-temperature phase up to 400 °C and the tetragonal high-temperature phase from 400 °C to 1000 °C. The electronic conductivity of PNCO was in the range of 65 â¤Â Ïe/S cmâ 1 â¤Â 90 (600-800 °C). The chemical surface exchange coefficient for oxygen (kchem) was obtained from in-situ dc-conductivity relaxation experiments between 600 °C and 800 °C and 10â 3 bar oxygen partial pressure. At temperatures close to 600 °C PNCO exhibited significantly faster oxygen exchange kinetics than the Co-free material Pr2NiO4 + δ (PNO). For example, the surface exchange coefficient of PNCO at 600 °C was around 2 Ã 10â 5 cm sâ 1, while kchem of PNO was approximately one order of magnitude smaller. However, at 800 °C both compounds showed similar oxygen exchange rates due to a lower activation energy of kchem for PNCO (~ 80 kJ molâ 1) as compared to PNO (~ 160 kJ molâ 1). Post-test analyses of the specimens used for conductivity relaxation measurements showed the formation of small Pr6O11 particles on the surface.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Solid State Ionics - Volume 316, March 2018, Pages 93-101
Journal: Solid State Ionics - Volume 316, March 2018, Pages 93-101
نویسندگان
Christian Berger, Edith Bucher, Andreas Egger, Anna Theresa Strasser, Nina Schrödl, Christian Gspan, Johannes Hofer, Werner Sitte,