Deposition of Gadolinia-Doped Zirconia Layers Using Metalorganic Compounds at Low Temperatures.

Agata Sawka

doi:10.3390/ma14247573

Abstract

This paper shows the results of an investigation on the synthesis of non-porous and nanocrystalline ZrO2-Gd2O3 layers by metalorganic chemical vapor deposition (MOCVD) with the use of Zr(tmhd)4 (tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)zirconium(IV)) and Gd(tmhd)3 (tris(2,2,6,6-tetramethyl-3,5-heptanedionato)gadolinium(III)). Argon and air were used as carrier gases. The molar content of Gd(tmhd)3 in the gas reaction mixture was as follows: 10% and 20%. The layers were synthesized on tubular substrates made of quartz glass at the temperatures of 550–700 °C. Synthesis conditions were established using the Grx/Rex2 expression (Gr is the Grashof number; Re is the Reynolds number; x is the distance from the gas inflow point). The value of this criterion was below 0.01. ZrO2-Gd2O3 layers synthesized at 600–700 °C were crystalline. When the molar content of Gd(tmhd)3 in the gas reaction mixture was 10 mol.%, a relationship between the chemical composition of the gas reaction mixture and that of the deposited layer could be observed. The synthesized layers underwent scanning electron microscopy, as well as X-ray analysis. The transparency of coated and uncoated glass was tested using UV–Vis spectroscopy. Their chemical composition was examined with the use of an EDS analyzer.

Highlights

ZrO2-Gd2O3 system materials exhibit very promising electrical, optical, thermal, and mechanical properties
This paper presents the results of research on the microstructure, structure, and chemical composition of Gd2O3-doped ZrO2 layers synthesized by metalorganic chemical vapor deposition (MOCVD) onto substrates of complex shape
The use of a high dilution of the reactants in the carrier gases, and/or the reduction of the diffusion coefficients of reactants, can cause a decrease in the transition temperature from the synthesis controlled by the reaction rate to that controlled by mass diffusion to the substrate from the gas phase

Summary

Introduction

ZrO2-Gd2O3 system materials exhibit very promising electrical, optical, thermal, and mechanical properties. They are characterized by good ionic conductivity, which means that they can be applied as an electrolyte in solid oxide fuel cells [1,2,3,4,5,6,7,8,9,10,11]; they can emit narrow bands in the UV-B region, which influences the luminescence properties of this material [12]; and they have high radiation resistance and can be used, for example, in the immobilization of nuclear waste products generated in nuclear reactor fuel [13]. A reduced fracture toughness, which leads to easy crack formation and lower erosion resistance [25,26] It seems [32] that the addition of YbSZ (Yb2O3-stabilized ZrO2) to Gd2Zr2O7 could improve its fracture toughness. The manufacturing and the properties of Gd2Zr2O7 coatings have been studied extensively for many years; investigations on the synthesis of Gd2O3-doped ZrO2 layers have been significantly less developed

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