Optical and structural investigation of the lanthanum β-alumina phase doped with europium

The lanthanum β-alumina phase doped with europium was investigated by X-ray diffraction and fluorescence. This nonstoichiometric phase exists over the composition range: $\text{11}\text{Al}{}_2\text{O}{}_3\text{1}\text{La}{}_2\text{O}{}_3$ to $\text{14}\text{Al}{}_2\text{O}{}_3\text{1}\text{La}{}_2\text{O}{}_3$. The unit cell is hexagonal hexagonal with a = 5.560 ± 0.003 Å, c = 22.001 ± 0.003 Å and belongs to the $\text{P6}{}_3\text{mmc}$ space group. X-ray diffraction patterns do not vary between both boundary compositions, but fluorescence spectra show that the structure of the mirror plane in which the lanthanide ions are located is deeply modified. The atomic structure of the mirror plane is of “β-type” (like β(Na) or β(Ag)) for the lower alumina contents; it gradually changes to a “magnetoplumbite type” for higher alumina contents.