METASTABILITY OF YTTRIUM OXIDES

Metastable yttrium oxide films are synthesized using reactive sputter deposition. The yttrium concentration of the as-deposited film is foun d to vary as a function of the sputter deposition rate. In addition to the synthesis of the cubic equilibrium phase Y2O3, oxide compounds ca n be formed with 40-80 at.% Y. The crystalline state of the as-deposit ed film is dependent on the substrate temperature. A metastable, ortho rhombic yttrium-rich oxide is formed on room temperature substrates. S ubstrates of Ta10W are coated with several micrometers of yttrium oxid e. The stability of these yttrium oxide coatings is investigated as th ey are subjected to an atmospheric pressure of oxygen at an elevated t emperature of 1773 K. The coatings and substrates are examined for the stability of the crystalline structure, composition, cracking, adhesi on and corrosion. An yttrium-rich oxide coating is found to offer the best corrosion protection to the Ta10W substrate.