Vaporization of Sr- and Mg-Doped Lanthanum Gallate and Implications for Solid Oxide Fuel Cells

Abstract

Vaporization of the La 0.85 Sr 0.15 Ga 0.85 Mg 0.15 O 2.85 , and La 0.90 Sr 0.10 Ga 0.80 Mg 0.20 O 2.85 perovskite phases was investigated by the use of Knudsen effusion mass spectrometry in the temperature range of 1618-1886 K. The partial pressures of the gaseous species O 2 , Mg, Sr, SrO, Ga, GaO, Ga 2 O, and LaO were determined over the samples investigated. The equilibrium partial pressures were used for the calculation of thermodynamic activities of the components at 1800 K. The results are compared with thermodynamic data of LaGaO 3 ͑s͒ without additives. Implications of the present data for the potential use of the material in solid oxide fuel cell technology are discussed as well.The La 1Ϫx Sr x Ga 1Ϫy Mg y O 3Ϫ(xϩy)/2 perovskite phase with different Sr and Mg content has recently been proposed as a possible candidate material for the electrolyte of solid oxide fuel cells ͑SOFC͒. 1 The material shows a good oxygen ion conductivity at about 800°C 2 which is comparable to that of ZrO 2 stabilized with 8 mol % Y 2 O 3 ͑YSZ͒ at 1000°C. The latter material is commonly used as the solid electrolyte in SOFCs. Electrolytes made of La 1Ϫx Sr x Ga 1Ϫy Mg y O 3Ϫ(xϩy)/2 are useful for low SOFC operating temperatures. Low operating temperatures between 750 and 800°C allow serious technological and chemical problems to be avoided. The study of the physicochemical properties of this compound is, therefore, of great practical interest. For example, the vaporization processes in the different atmospheres at the anode and cathode sides of the SOFC have to be known under operating conditions. It has been shown that lanthanum gallate vaporizes incongruently, 3,4 which can lead to changes in the chemical composition of the electrolyte and, as a consequence, to a change of its chemical and electrochemical properties. Knowledge of the potential for the decrease of this vaporization by the use of a doped LaGaO 3 ceramic electrolyte is, therefore, of practical interest. There are no studies to date dealing with the influence of the partial substitution of alkaline earth metals for La and Ga in LaGaO 3 on the volatility of the doped material.A further problem might be the alkaline earth carbonate formation in LaGaO 3 base electrolytes if H 2 /CO anode gases are used. 5 Thermodynamic activities of the alkaline earth metal oxides SrO and MgO in La 1Ϫx Sr x Ga 1Ϫy Mg y O 3Ϫ(xϩy)/2 have to be known in order to make predictions about carbonate formation. 6 This paper reports on experimental investigations of the vaporization of the La 1Ϫx Sr x Ga 1Ϫy Mg y O 3Ϫ(xϩy)/2 perovskite phase carried out by Knudsen effusion mass spectrometry. Thermodynamic activities of oxide components in La 1Ϫx Sr x Ga 1Ϫy Mg y O 3Ϫ(xϩy)/2 are determined. The results are used to predict the vaporization of La 1Ϫx Sr x Ga 1Ϫy Mg y O 3Ϫ(xϩy)/2 under SOFC operating conditions at the anode and cathode sides. Implications of the data for the potential use of La 1Ϫx Sr x Ga 1Ϫy Mg y O 3Ϫ(xϩy)/2 in SOFC technology are discussed. ExperimentalTwo samples of the compo...

Thermodynamic and Cation Diffusion Studies of Perovskites on the Basis of LaGaO3 and Implications for SOFC

“…5. Mg , Sr , and SrO were additionally detected on vaporizing samples which contain the additives Mg and/or Sr.…”

Single-phase ceramics with La1−xSrxGa1−yMgyO3−δ composition from precursors obtained by mechanosynthesis

“…Its presence can thus facilitate the creation and propagation of cracks through the ceramics. Classical synthesis method by solid-state reaction (SSR) involves high sintering temperatures that do not fully eliminate the secondary phases and that can lead to compositional inhomogeities due to Ga evaporation [10].…”

Microstructure and Conductivity of La1−xSrxGa0.8Mg0.2O3−δ Electrolytes Prepared Using the Freeze-Drying Method

“…7(a) and (c)). 33 The influence of both Sr content and sintering time on the microstructure of LSGM materials was also examined. 7(d)).…”