Metastability of yttrium oxides

Metastable yttrium oxide films are synthesized using reactive sputter deposition. The yttrium concentration of the as-deposited film is found to vary as a function of the sputter deposition rate. In addition to the synthesis of the cubic equilibrium phase Y 2O 3, oxide compounds can be formed with 40–80 at. % Y. The crystalline state of the as-deposited film is dependent on the substrate temperature. A metastable, orthorhombic yttrium-rich oxide is formed on room temperature substrates. Substrates of Ta 10W are coated with several micrometers of yttrium oxide. The stability of these yttrium oxide coatings is investigated as they are subjected to an atmospheric pressure of oxygen at an elevated temperature of 1773 K. The coatings and substrates are examined for the stability of the crystalline structure, composition, cracking, adhesion and corrosion. An yttrium-rich oxide coating is found to offer the best corrosion protection to the Ta 10W substrate.