All studied glasses have been prepared by flame synthesis from polycrystalline precursor powders of corresponding compositions by flame synthesis. The precursor powders were synthesized with the use of a modified Pechini synthesis [19]. Required metal nitrates (i.e., aluminium nitrate and the respective rare earth nitrates, all of the p.a. quality) were dissolved in deionized water and mixed. Then, an aqueous solution of citric acid and ethylene glycol (in the molar ratio 1:1) was added to the solution of nitrates. The resulting solution was refluxed at 85 ◦ C for 2 h and then heated to 150 ◦ C to promote polymerization (solution viscosity increased rapidly) and solvent evaporation until an aerated resin was formed. Finally, the organic compounds were removed by heating to 800 ◦ C for 6h. The synthesized precursor powders were then crushed, sieved through a 40 m polyethylene mesh screen and fed into methane–oxygen flame [12]. In the flame the powder particles melted. The molten droplets were sprayed with distilled water ensuring the estimated cooling rate of 1000 ◦ C s−1 . Spherical glassy particles formed, which were then collected in a sedimentation tank, separated, dried and calcined at 650 ◦ C. The morphology of the microspheres was examined by optical microscopy (Nikon ECLIPSE ME 600) in transmitted light, and by SEM analysis (JEOL 7600f) at the 20 kV accelerating voltage. The crystallization properties of prepared glasses were studied by simultaneous thermal analysis (STA), and high temperature X-Ray diffraction (HT-XRD).