Structural characteristics and thermal properties of gadolinium zirconate thin films processed by Direct Liquid Injection Chemical Vapor Deposition

Abstract

Gadolinium zirconate Gd₂Zr₂O₇ coatings were deposited by an original route based on Direct Liquid Injection Metal Organic Chemical Vapor Deposition (DLI-MOCVD) at the relatively low temperature of 550 °C. By using the heteroleptic precursor [Zr(OiPr)₂(tbaoac)₂] combined with tris(2,2,6,6-tetramethyl-3,5-heptanedionato) gadolinium(III) [Gd(thd)₃] and O₂, polycrystalline coatings of Gd₂Zr₂O₇ of columnar structure composed of the pyrochlore and fluorite phases were deposited on silicon and steel substrates. Deposition rates as high as 1 μm/h were obtained, allowing to produce coatings reaching 25 μm in thickness, with mean roughness lower than 1 μm. Their thermal characterization was performed using modulated photothermal radiometry (MPTR). The coating thermal resistances appeared to be influenced by several factors, in particular the crystalline quality related with the presence of the pyrochlore and fluorite phases and the Gd/Zr ratio. The most crystallized coatings presenting the smallest column width and the highest Gd/Zr ratio provided the lowest apparent thermal conductivities, competing with the best results of the literature. This DLI-MOCVD route was developed with the objective to coat the internal surface of thermosensitive steel substrates of interest for plastic injection molding. By delaying heat transfer at the molten polymer/mold interface, such ceramic coatings could prevent premature solidification of the polymer melt, contributing to reduce part rejection. They could also be of interest for other applications needing efficient thermal barrier coatings for mild temperature use (energy, electronics, automotive, …).