Some observations on synthesis and electrolytic properties of nonstoichiometric calcium zirconate

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• 作者：Magdalena Dudek ; Ewa Droż ; dż ; -Cieś ; la
• 关键词：Electrolyte ; Perovskites ; Co-precipitation method ; Ionic conduction
• 刊名：Journal of Alloys and Compounds
• 出版年：2009
• 出版时间：5 May 2009
• 年：2009
• 卷：475
• 期：1-2
• 页码：846-854
• 全文大小：1534 K

文摘

Stoichiometric CaZrO₃ (CZ-50) and CaZrO₃ doped with excess CaO (CZ-51) powders, whose formula (CaO)_1−x(ZrO₂)_x, where x = 50 or 51 mol. % CaO was successfully synthesised by the co-precipitation calcination method with a saturated solution of (NH₄)₂C₂O₄ in concentrated NH₃ solution as a precipitation agent. The thermal evolution of CaZrO₃ dried precursor during heating them up to 1200 °C was monitored by thermal (DTA, TG) and X-ray diffraction analysis methods. The highest temperature (1200 °C) for CaZrO₃ synthesis was found for stoichiometric CaZrO₃, whereas introduction of excess CaO into CaZrO₃ led to a decrease in the synthesis temperature to 1000 °C. The crystallite size d_(h k l) of grounded CaZrO₃ powders ranged from 43 to 90 nm, respectively. BET measurements indicated that in both the investigated powders, particles were agglomerated. Sintering CaZrO₃-based samples at 1500 °C/2 h or hot-pressing process (1250 °C/1 h, 25 MPa) was applied to obtain gas-tight CaZrO₃-based ceramics. To examine the thermochemical stability of materials obtained at high temperatures, the CaZrO₃-based samples were additionally heated at 1200 °C for 120 h or in the temperature range 1400–1600 °C for 24 h in air or purified argon. There were also performed and then discussed, some tests on thermal resistance of CaZrO₃ against molten metals—nickel and copper. Investigations into chemical reactivity of CaZrO₃ electrolyte with electrode materials involving LaCrO₃ or MCr₂O₄ (M = Mg, Ca) in the temperature range 1000–1200 °C were conducted using XRD with Rietveld analysis. Electrical conductivity measurements performed by both dc and ac impedance spectroscopy method in the temperature range 200–1000 °C. The best oxygen ion conductivity was found for CaZrO₃-doped excess CaO (CZ-51) samples sintered in air, starting from powders synthesized by co-precipitation or citrate method. The CZ-51 samples obtained via solid state reaction or hot-pressed exhibited lower values of electrical conductivity. Test results for this compound used as an electrolyte in solid oxide cells involving electrode materials MCr₂O₄ (M = Mg, Ca) are also reported. In this way the Gibbs free energy of formation of MgCr₂O₄ at 1000 °C was determined. The nonstoichiometric CaZrO₃ seems to be a promising solid electrolyte for electrochemical oxygen probes in control of metal processing.