AVS 46th International Symposium
    Vacuum Metallurgy Division Wednesday Sessions
       Session VM-WeM

Paper VM-WeM3
High Refractive Index <100>-Textured Cubic Zirconia Formed in Nanolaminate Coatings Using Titania Interruption Layers

Wednesday, October 27, 1999, 9:00 am, Room 620

Session: Advanced Surface Treatments and Coatings
Presenter: J.D. DeLoach, University of Wisconsin, Milwaukee
Authors: J.D. DeLoach, University of Wisconsin, Milwaukee
C.R. Aita, University of Wisconsin, Milwaukee
Correspondent: Click to Email
Thermodynamic phase evolution of bulk zirconia cooled from the liquidus (2680 @super o@C) is as follows: cubic (2360 @super o@C) to tetragonal (~1075 @super o@C) to monoclinic (STP phase). However, the pseudobinary zirconia-yttria phase diagram shows that the cubic phase is stabilized at room temperature by adding approximately 10 mole % yttria. Therefore, most reports of cubic zirconia formation in coatings of practical thickness involve yttria-doped zirconia. Undoped zirconia single layer film studies report the transformation from cubic to monoclinic zirconia with increasing crystallite size, suggesting that a finite crystal size effect aids in cubic zirconia stabilization. For this reason, zirconia phase control is easier in a multilayer scheme, by the introduction of growth interruption layers. This approach was taken by several investigators who grew cubic zirconia in zirconia/yttria nanolaminates. In these cases, cubic zirconia was formed by heteroepitaxy with either <111>-texture cubic yttria or a <111>-texture interfacial cubic zirconia-yttria alloy. The drawbacks of using yttria for growth interruption layers were: (1) the refractive index of the nanolaminate was considerably lowered by the presence of yttria, and (2) the <111>-texture of cubic zirconia was stabilized by heteroepitaxy, precluding a <100>-texture desirable for certain applications. In this study, a sputter-deposited nanolaminate structure consisting of polycrystalline zirconia-vitreous titania bilayers was used to fabricate high refractive index, undoped cubic zirconia coatings with a strong <100> crystallographic texture. Titania was chosen as the interruption layer material because: (1) its vitreous nature encouraged low surface energy {200} cubic zirconia planes to preferentially orient parallel to the growth interface, resulting in a <100>-texture, and (2) its high refractive index resulted in a nanolaminate with an overall refractive index of 2.23.