Low temperature synthesis of nanocrystalline lanthanum monoaluminate powders by chemical coprecipitation

Nanocrystalline lanthanum monoaluminate (LaAlO₃) powders were prepared by chemical coprecipitation using 25 vol.% of NH₄OH, 0.05 M La(NO₃)₃·6H₂O and 0.05 M Al(NO₃)₃·9H₂O aqueous solutions as the starting materials. Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analyses (TGA/DTA), X-ray diffraction (XRD), Raman spectrometry, specific surface area (BET) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron diffraction (ED) were utilized to characterize the LaAlO₃ powders prepared by chemical coprecipitation. The crystallization temperature of the LaAlO₃ precursor gels precipitated at pH 9 is estimated as 810 °C by TG/DTA. The XRD pattern of the LaAlO₃ precursor gels precipitated at pH 8–12 and calcined at 700 °C for 6 h shows a broad arciform continuum exist between 24° and 32° and sharp peaks of LaAlO₃ except the precursor gels precipitated at pH 9. For the LaAlO₃ precursor gels precipitated at pH 9 and calcined at 700 °C for 6 h, the formation of the perovskite LaAlO₃ phase occurs and the presence of crystalline impurities is not found. The crystallite size of LaAlO₃ slightly increases from 37.8 to 41.5 nm with calcination temperature increasing from 700 to 900 °C for 6 h. The LaAlO₃ powders prepared by chemical coprecipitation have a considerably large specific surface of 30 m²/g. The relative density greater than 97% is obtained when these nanocrystalline LaAlO₃ powders are sintered at 1550 °C for 2 h.