Structural properties of Al2O3–La2O3 binary oxides prepared by sol–gel

The structural properties of La 2 O 3 and Al 2 O 3 –La 2 O 3 binary oxides prepared by sol–gel were studied by XRD, HRTEM and UV–vis. The binary oxides with high lanthana contents show an amorphous structure after calcination at 650 °C. At calcination temperatures higher than 1000 °C there is a phase transformation from the amorphous state to the crystalline LaAlO 3 with a perovskite structure. The structure of La 2 O 3 is consistent with the hexagonal system; however, some crystalline microdomains with a monoclinic structure were detected by HRTEM. Islands of La 2 O 3 and LaAl 11 O 18 phases were detected at high lanthana concentration in the binary oxide. The modification in the coordination shell of the Al 3+ cations due to the interaction with La 3+ cations confirms the formation of phases with a perovskite structure and the presence of islands of the LaAl 11 O 18 phase.