Thermal analysis of metal organic precursors for functional oxide preparation: Thin films versus powders

• Accurate predictions require thermal analysis on thin films.
• Thin films usually decompose at a lower temperature than powders.
• Intermediate phases are less stable in thin films.
• Combustion processes are precluded in thin films.
• Synthesis of YBCO impossible from TFA precursor powders.

The thermal decomposition of several metal organic precursors, used in the preparation of YBa2Cu3O7−x superconducting coated conductors (Cu acetate, Cu, Y and Ba trifluoroacetates and Ce propionate) is analyzed by means of several thermoanalytical techniques (TG/DTA, MS and DSC). In all cases, the metal organic precursors deposited as thin films decompose differently than powders from the same precursors. In thin films, decomposition is facilitated by the easier transport of reactive gas from the surrounding atmosphere and by the easier out-diffusion of volatile products. Consequently, films decompose at lower temperature and are more sensitive to the presence of any residual reactive gas in the furnace. Good thermal contact with the substrate is also shown to minimize overheating in films and avoid combustion processes that are otherwise often observed during the thermal decomposition of powders. Finally, the formation and stability of intermediate products towards the oxide formation, such as metal fluorides, differs in films because of the easier gas exchange. With respect to powders, these compounds are much less stable in films, where their decomposition temperature can be lowered by several hundreds of degrees Celsius. While in some cases the behaviour of films can be predicted by analyzing varying masses of precursor powders, this is not always the case. Therefore, thermal analysis carried out on films is recommended to avoid erroneous conclusions about materials preparation drawn from powders.

Decomposition of metal organic precursors often depends on one transport step. Since transport is easier in films than in powders, caution should be paid to thermal analysis of powders when applied to films.Figure optionsDownload as PowerPoint slide