本研究以LaAlO3為主，以硝酸鑭及硝酸鋁為起使原料，藉由添加檸檬酸鏊合金屬離子，探討[金屬] / [檸檬酸]比和煆燒氣氛（空氣或氧氣氛）、溫度與時間對金屬檸檬酸鹽先驅物熱解製得結晶LaAlO3奈米粉體的影響。研究中利用熱重分析/熱差分析儀(TGA /DTA)的結果來判別在不同煆燒氣氛下的熱行為，且以傅氏轉換紅外線光譜儀（FT-IR）與X-光線繞射分析(XRD)結果來探討鋁酸鑭的成相過程。並利用掃瞄式電子顯微鏡(SEM)與穿透式電子顯微鏡(TEM)來觀察粉末形態。 當[檸檬酸]/[金屬]=2.25(CA2.25)且不添加氨水的系統中，經過350℃熱處理之後，鑭離子和鋁離子會形成LaAl(OOCH2)3的鍵結，而起始溶液添加氨水則會形成LaAlO3-x(CO3)x(s)。當檸檬酸量的減少[檸檬酸]/[金屬]=0.5 (CA0.5)，可降低碳酸根的含量，其熱行為與CA2.25相似；但兩系統皆需煆燒≥ 800℃才能移除殘留的焦碳得到純的LaAlO3。熱處理時，在氧氣氛下可降低結構中的氧空缺，使結晶峰的溫度提前，促使CA0.5 pH7檸檬酸鹽固態先驅物在氧氣氛下550℃ 3小時後即可得結晶的LaAlO3。顯結構分析顯示，不添加氨水時，減少檸檬酸的添加有助於減少塊體凝聚的現象；添加氨水時，檸檬酸過量系統呈現塊狀，且較為緊密，CA0.5則較為鬆散。隨著氨水的添加量增加有助於縮小粉體晶粒尺寸。 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.
