Synthesis of Doped Lanthanum Gallium Oxide by Metastable Intermediate Phase Method and Its Application as Electrolytes for Intermediate Temperature SOFC
Date Issued
2015
Date
2015
Author(s)
Hsu, Chien-Lun
Abstract
The purpose of this thesis is to prepare La1-xSrxGa1-yMgyO3-δ (LSGM) of pure perovskite phase for the use as the electrolyte material of intermediate temperature solid oxide fuel cell. However, it has been difficult to prepare LSGM of pure phase by one pot method. Several secondary phases, such as LaSrGaO4, LaSrGa3O7, and La4Ga2O9, were frequently formed. Nevertheless, pure perovskite phase of LaGa0.9Mg0.1O3-δ material could be obtained, where Sr was not present, suggesting that the Sr dopant is probably the reason of the formation of secondary phases. Among the secondary phases, La4Ga2O9 could be removed by sintering repeatedly at high temperatures, while the other two phases containing Sr could not. These results suggested that Sr and Ga prefer to react and form stable secondary phases, which cannot further react. Therefore, a metastable intermediate method was developed to prepare La1-xSrxGa1-yMgyO3-δ of pure perovskite phase by two-steps reactions. Electrolyte materials were prepared by separating Sr and Ga elementsand synthesizing the intermediate phases first. Then, the other components were incorporated in the second steps. By choosing the intermediate phases with Ga but without Sr, two intermediate phases, LaGaO3 and MgGa2O4, were prepared. Indeed, La1-xSrxGa1-yMgyO3-δ of pure perovskite phase was successfully prepared by using these two intermediate. The highest ionic conductivities were observed on samples La0.75Sr0.25Ga0.67Mg0.33O3-δ and La0.75Sr0.25Ga0.75Mg0.25O3-δ prepared by LaGaO3 and MgGa2O4 intermediate phases with conductivities of 0.044 and 0.075 Scm-1, respectively.
Subjects
IT-SOFC
LGO
Type
thesis