Phase partitioning and epitaxy of Zr(Al)O2 thin films on cubic zirconia substrates

Abstract

Thin films of ZrO₂-Al₂O₃ were grown on cubic-Zr(Y)O₂ substrates by a liquid precursor route. Phase formation and epitaxy of these films was studied as a function of heat-treatment temperature and time. The following sequence of phases was observed in these thin films: Precursor → t-(Zr,Al)O₂ → t-(Zr,Al)O₂ + γ-(Al,Zr)₂O₃ → m-ZrO₂ + α-Al₂O₃ Observations strongly suggest that the epitaxial process initiated before the metastable, single phase t-(Zr, Al)O₂ partitioned to t-(Zr, Al)O₂ + γ-(Al, Zr)₂O₃. Observations at 1400 °C show that, after the γ to α transformation, α-Al₂O₃, grains develop an elongated, prismatic morphology and an epitaxial relation with the underlying and surrounding m-ZrO₂. The phase that is chemically and structurally similar to the substrate, in this case t-(Zr,Al)O₂, or m-ZrO₂, forms an epitaxial layer between the substrate and isolated, prismatic grains of heteroepitaxial α-Al₂O₃.