Pulsed Injection MOCVD of YSZ Thin Films onto Dense and Porous Substrates^†

In this work, we describe the preparation of YSZ layers on dense and porous substrates using the pulsed injection metal–organic (MO) CVD technique. In this technique, the vapor phase is obtained by injecting micro-droplets of a solution, consisting of the required amounts of Zr(tmhd)₄ and Y(tmhd)₃ precursors in monoglyme, into a heated evaporator. The droplet characteristics (volume, precursor concentration, and injection frequency) were studied in order to control the growth rate and the microstructure of the layers. The optimum deposition parameters needed to achieve dense film microstructure on dense substrates were determined. For these optimized experimental conditions, we evaluated the growth rate of the layers as a function of temperature. The activation energy in the kinetically limited regime was found to be 96 kJ mol^–1. The structure of the layers was analyzed as a function of the film composition. A concentration of 11 mol-% of yttria fully stabilizes the cubic phase. This process has been applied to the preparation of dense YSZ membranes on porous substrates in order to use the YSZ layer as a solid electrolyte (SE) in electrochemical devices such as solid oxide fuel cells (SOFC), oxygen sensors, and generators. Dense YSZ layers were obtained on samples of porous alumina, and on YSZ-Ni cermets. Characterization by scanning electron microscopy (SEM) and X-ray diffraction (XRD) showed no cracks or voids along the grain boundaries, nor secondary phases due to chemical interaction with the substrate.