Study on the Al 2O 3–SiO 2–La 2O 3 ternary system at 1300°C

Abstract

The ternary phase diagram Al 2O 3–SiO 2–La 2O 3 was investigated at 1300°C. The samples were prepared by wet chemical route (sol-gel synthesis) and characterized by differential thermal analysis (DTA), X-ray diffraction (XRD), and EDX microprobe analysis. The XRD powder pattern data of La 14Si 9O 39 compound, as obtained by us, reconfirm the structure proposed in the literature, though with significantly different lattice parameters. No truly ternary compound was found to form at 1300°C. The La 14Si 9O 39 compound extends its stability range in the interior of the phase diagram, forming a solid solution of the type La 14+x/3Si 9−x Al xO 39, which is stable from x = 0 to x = 1.5. This substitutional stoichiometry can be described as a tetrahedral Al for Si substitution on the 6 h position and contemporary occupation of vacant La sites.