Preparation, Structure And Properties Of La_1-xSr_xGa_1-yMg_yO₃ Solid Electrolytes

Perovskite-type complex oxides of La1-xSrxGa1-yMgyO3 compositions are characteristic of superior intermediate temperature oxide-ion conductivity and chemical stability, which are expected to be used in solid oxide fuel cells, sensors, electrocatalysis, membrane separators and membrane reactors. They have highly promising prospects in energy, metallurgy, chemical engineering and environmental protection, etc. In this dissertation, improved embeded sintering method has been employed to prepare La0.8Sr0.2Ga1-yMgyO3 (LSGM)electrolyte, and the contributing factors to preparation, microstructure characteristics, conduction properties and thermology properties of LSGM electrolyte have been investigated. The relationships between the composition, structure and conduction properties have been studied, and the ionic conduction mechanism in LSGM electrolyte has been discussed.The solid reaction synthetic process, sintering properties and phase composition of the LSGM samples are investigated by TG-DTA, SEM, XRD and the Archimedes method. The results reveal that the sintering technology generated significant influence on the sintering properties of the LSGM samples. The optimum synthesis parameters to prepare LSGM electrolyte with a pure perovskite-type structure were ascertained; The sintering temperature and chemical constitution contributed greatly to the phase composition, the solid solubility limit of LSGM electrolyte increased with increasing of the sintering temperature, and we made LSGM electrolyte of single-perovskite structure above 1400#. the solid solubility limit of Mg in La0.8Sr0.2Ga1-yMgyO3 electrolyte is about 40% at the substitution site.The ionic conductivity of La0.8Sr0.2Ga1-yMgyO3 electrolyte was investigated using two-probe ac impedance technique. The ionic conduction properties of the ceramic samples depended closely on sintering temperature and sintering time, which reached an optimum value at 1470# for 18h. At an identical measuring temperature, the electrical conductivity of La0.8Sr0.2Ga1-yMgyO3 electrolyteincreased with the Mg doping content, up to its maximum value at y=0.2, and then decreased. The ionic conductivities of LSGM enhanced with the measuring temperature.Based on the results of electrical measurements, the relative contribution of the grain interior and grin boundaries to the overall resistance was discussed in detail in relation with the grain boundary effect and Mg doping contents. The grain boundary effect decreased monotonously with the increase of Mg doping in the range of testing temperature. And the ionic conduction mechanism in LSGM electrolyte varied with the Mg doping.The measurement results of thermal expansion coefficients and TG-DSC of the LSGM samples showed that the thermal expansion coefficients of La0.8Sr0.2Ga1-yMgyO3 electrolyte increased with the increasing of the Mg doping, so we can control the thermal expansion coefficients of LSGM electrolyte through adjusting the Mg doping content. And the LSGM was essentially stable over temperature from 500 to 800, in which SOFC of intermediate temperature operates one.