Effects of atmosphere of calcination on the formation of crystalline LaAlO3 derived from the citrate precursor method

• Main Authors: Yu-Man Kuo, 郭于嫚
• Other Authors: Hsuan-Fu Yu
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/11258014184923074787

碩士 === 淡江大學 === 化學工程與材料工程學系碩士班 === 96 === The reaction mechanisms for forming pure LaAlO3 from the citrate-precursors, being derived from the aqueous solutions containing La(NO3)3, Al(NO3)3, and C3H4(OH)(COOH)3 in different molar ratio at different pH conditions, and effects of atmosphere、temperature and time of calcination, were investigated using x-ray diffractometry, infrared spectroscopy, thermogravimetric analysis, and differential thermal analysis. The particle size and morphology of LaAlO3 powder were observed using scanning electron microscopy and transmission electron microscopy. At 350 oC, the lanthanum and aluminum elements were bonded together in forms of LaAl(OOCH2)3 for no NH4OH additions and LaAlO3-x-y(CO3)x(OH)2y for adding NH4OH in the starting solution. The specimen derived using [Citric Acid]/[Metallic ions]=0.5(CA0.5) has less cher formation than those using [Citric Acid]/[Metallic ions]=2.25(CA2.25), and the thermochemical behavior for different citric acid additions are similar. However, calcining the specimens at ≥ 800 oC were required to remove all residual chars in air atmosphere to form pure LaAlO3. When calcined in oxygen the specimens may contain less amount of oxygen vacancies in the structure, which make the citrate-precursor CA0.5 pH7 can form crystalline LaAlO3 at 550℃ for 3hr. From the SEM and TEM observations, the powder obtained by adding NH4OH has a less degree of particle agglomeration than that obtained without NH4OH addition.The grain size of LaAlO3 decrease with the NH4OH additions, for the powder calcined at 900℃ for 3 h.