Thermal stability of ortho-aluminates of yttrium subgroup rare earths

Temperature dependence of the stability of rare earth oftho-aluminates LnAlO3 (Ln=Gd, Ho, Er, Tm, Yb, Lu and Y) is studied and its connection with phase diagrams of the oxide systems is established. In the range of 1100-1300 deg C all the polycrystal ortho-aluminates decompose according to the 7LnAlO3 (perovskite structure) →Ln3Al5O12 (garnet structure)+Ln4Al2O3 (monoclinic structure) reaction. Intensity of decomposition of lutecium subgroup aluminates (l.s.g.) increases with the temperature increase and at 1400 deg a complete decomposition of these compounds takes place. The complete decomposition of yttrium subgroup aluminates(y.s.g.) has not been reached. L.s.g. single crystal aluminates decompose according to the 5LnAlO3→Ln3Al5O12+Ln2O3 reaction