التفاصيل البيبلوغرافية
| العنوان: |
Synthesis and characterization of the novel K2NiF4-type oxide Pr2Ni0.9Co0.1O4 + δ. |
| المؤلفون: |
Berger, Christian1, Bucher, Edith1 edith.bucher@unileoben.ac.at, Egger, Andreas1, Strasser, Anna Theresa1, Schrödl, Nina1, Gspan, Christian2, Hofer, Johannes1, Sitte, Werner1 |
| المصدر: |
Solid State Ionics. Mar2018, Vol. 316, p93-101. 9p. |
| مصطلحات موضوعية: |
*OXIDE synthesis, *DRYING, *FREEZING, *X-ray diffraction, *RIETVELD refinement, *THERMOGRAVIMETRY, *PHASE transitions |
| مستخلص: |
Pr 2 Ni 0.9 Co 0.1 O 4 + 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% Pr 6 O 11 as secondary phase) with an orthorhombic K 2 NiF 4 -type unit cell at room temperature. Precision thermogravimetry between 30 °C and 900 °C showed an irreversible mass increase at T ≥ 750 °C and p O 2 = 0.2 bar which indicated the transition to a higher order Ruddlesden-Popper phase Pr 4 (Ni,Co) 3 O 10 − x and PrO y . Differential scanning calorimetry in pure Ar and 20% O 2 /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 × 10 − 3 ≤ p O 2 /bar ≤ 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 ≤ σ e /S cm − 1 ≤ 90 (600–800 °C). The chemical surface exchange coefficient for oxygen ( k chem ) was obtained from in-situ dc-conductivity relaxation experiments between 600 °C and 800 °C and 10 − 3 bar oxygen partial pressure. At temperatures close to 600 °C PNCO exhibited significantly faster oxygen exchange kinetics than the Co-free material Pr 2 NiO 4 + δ (PNO). For example, the surface exchange coefficient of PNCO at 600 °C was around 2 × 10 − 5 cm s − 1 , while k chem 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 k chem for PNCO (~ 80 kJ mol − 1 ) as compared to PNO (~ 160 kJ mol − 1 ). Post-test analyses of the specimens used for conductivity relaxation measurements showed the formation of small Pr 6 O 11 particles on the surface. [ABSTRACT FROM AUTHOR] |
| قاعدة البيانات: |
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