Thermochemical behavior of metallic citrate precursors for the production of pure LaAlO3

Pure LaAlO3 nanoparticles were synthesized, using a citrate-precursor technique. La(NO3)3, Al(NO3)3, and C3H4(OH)(COOH)3, in a molar ratio of 1:1:4.5, were dissolved in deionized water. The pH of the aqueous solution was adjusted using NH4OH. After drying, the citrate precursors were charred at 350 °C, followed by calcination at different temperatures. The thermochemical behavior of the charred citrate precursor to form LaAlO3 was investigated using X-ray diffractometry, infrared spectroscopy, thermogravimetric analysis, and differential thermal analysis. While the charred specimen obtained at pH=2 (without NH4OH addition) was composed of LaAl(OOCH2)3, the charred specimens obtained at pH>2 were composed of LaAlO3−x−y(CO3)x(OH)2y. All these metallic salts were decomposed at temperatures between 600 and 780 °C to form crystalline LaAlO3 but calcining the specimens in air at ⩾800 °C were required to remove all residual chars to produce pure LaAlO3. At 900 °C, the citrate-derived particles obtained at pH>2 were composed of LaAlO3 crystallites with an average size of ∼30 nm.