To see if the synthesized powder can be used directly for crystal growth, a pressed pellet was placed in an Al 2 O 3 boat on a bed of extra powder in a GSL-1700X tube furnace. After 3 h of heating in air at 1650 • C and cooling to room temperature, the pellet appeared to have melted. The product was mechanically removed from the boat, and powder XRD showed that the result was a mixture of Eu-Al-O compounds (see Supporting Information, Figure ). Decomposition may have allowed B 2 O 3 to evaporate because of its high vapor pressure, or it may have been present in an amorphous form. Therefore, the microwave powder was confirmed to be incongruently melting and would be difficult to use for methods such as float zone, Bridgman, or Czochralski crystal growth. Still, the powder was used for several flux crystal growths in place of the stoichiometric oxide mixture, producing well-faceted crystals.