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.