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

We acknowledge the financial support from MICINN (MAT2011-28874-C02-01 and -02, Consolider Project NANOSELECT: CSD2007-00041), EU project EUROTAPES, (EUFP7 NMPLA2012280432) and by the Generalitat de Catalunya (Pla de Recerca 2009SGR-185, 2009-SGR-770 and XaRMAE). H. Eloussifi acknowledges financial support from the Tunisian Ministry of Higher Education and Scientific Research