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 LaAlO_3−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.