Crystallization and Grain Growth Kinetics for Precipitation‐Based Ceramics: A Case Study on Amorphous Ceria Thin Films from Spray Pyrolysis

Abstract

The introductory part reviews the impact of thin film fabrication, precipitation versus vacuum‐based methods, on the initial defect state of the material and microstructure evolution to amorphous, biphasic amorphous‐nanocrystalline, and fully nanocrystalline metal oxides. In this study, general rules for the kinetics of nucleation, crystallization, and grain growth of a pure single‐phase metal oxide thin film made by a precipitation‐based technique from a precursor with one single organic solvent are discussed. For this a complete case study on the isothermal and non‐isothermal microstructure evolution of dense amorphous ceria thin films fabricated by spray pyrolysis is conducted. A general model is established and comparison of these thin film microstructure evolution to kinetics of classical glass‐ceramics or metallic glasses is presented. Knowledge on thermal microstructure evolution of originally amorphous precipitation‐based metal oxide thin films allows for their introduction and distinctive microstructure engineering in devices‐based on microelectromechanical (MEMS) technology such as solar cells, capacitors, sensors, micro‐solid oxide fuel cells, or oxygen separation membranes on Si‐chips.

Development of CO2 Protective Layers by Spray Pyrolysis for Ceramic Oxygen Transport Membranes

“…Although theoretically a (111) orientation is predicted, these (200) ceria textured fi lms have been observed previously on different substrates deposited by different techniques. [27][28][29][30][31] As previously reported, [ 27 ] it seems that there is a clear effect of the precursor/solvent on the texture [ 31,32 ] whilst grain size growth takes place after treatment above 800 ° C, as also observed elsewhere. [ 32 ] According to the AFM and optical refl ectometry data, the as-deposited CGO thin fi lms are smooth and present a surface roughness of Ra ≈ 7 nm and grain sizes around 20 nm.…”

Time–Temperature–Transformation (TTT) Diagrams for Crystallization of Metal Oxide Thin Films

“…In contrast to classical glass-ceramic or metallicglass TTT diagrams, where the cooling curves are registered for transformation from the undercooled liquid to the crystalline state, the thin fi lms crystallize upon heating to temperatures higher than their thin-fi lm deposition The plots display the thermokinetics of crystallization of the original amorphous thin fi lms indicated by the degree of crystallinity in percentage. The important key temperatures for their crystallization are the deposition temperature ( T d ), crystallization peak temperature ( T p ) (determined by DSC from the exothermic heat loss [ 13 ] ) and the crystallization end temperature ( T e ). For T < T p mostly nucleation is ongoing and the crystallization rates are similar for both the undoped and doped thin fi lms.…”

“…Recently, amorphous metal oxide thin fi lms have been reported to exhibit similar crystallization kinetic rules and characteristics as glass-based systems, [ 13 ] for instance, Kissinger crystallization activation energies between 1-3 eV, [ 14 ] JohnsonMehl-Avrami characteristics, [ 15 , 16 ] and crystallization enthalpies around 90-100 J g −1 .…”

“…[ 13 ] A metal oxide thin fi lm crystallizes directly within the solid structure when heated above its fi lm deposition temperature similar to a glass thin fi lm. These metal oxide thin fi lms exhibit dense and amorphous microstructures directly after fi lm deposition whereby they remain in a solid state for the full transition from the amorphous to the fully crystalline state.…”

“…[ 13 ] Both amorphous metal oxide thin fi lms and glassy materials show crystallization behavior that is purely driven by the reduction of the volume free energy in the transformation of amorphous to crystalline. [ 13 ] A metal oxide thin fi lm crystallizes directly within the solid structure when heated above its fi lm deposition temperature similar to a glass thin fi lm.…”