Fabrication of transparent ceramics through melt solidification of near eutectic compositions in HfO2–Al2O3–GdAlO3 system

Solidification of eutectic melts in multiple oxide systems can produce directionally solidified eutectic composites by slow cooling, while rapid cooling would give the formation of amorphous phases as super cooled liquids. We have successfully fabricated an amorphous bulk ceramics in the ternary system HfO2–Al2O3–GdAlO3 for the first time. It has the near eutectic composition of HfO2 (14 mol%), Al2O3 (63 mol%) and Gd2O3 (23 mol%) and highly transparent, >85%, in the visible region after the cooling of around 200–500 K/s for 2–5 mm Ø globules. The sample had kept amorphous up to 1073 K but crystallized above 1273 K then lost the transparency. The formation of an amorphous phase could be discussed by the equilibrated temperature (T0) lines in meta-stable phase diagram. The present study suggests possible formation of transparent bulk ceramics by the melt-solidification of eutectic melts in various ternary or multiple phase systems.