Degradation mechanisms when films of YBa2Cu3O7-x (YBCO) were formed on sapphire substrates have been studied. The films were synthesized by post-deposition annealings in a wet oxygen atmosphere of coevaporated layers of Y-BaF2-Cu-O. X-ray diffraction revealed the existence of impurity phases in the annealed samples, the most significant being BaAl2O4, Y2BaCuO5, CuO and Y2O3. Redistribution of the constituents as a function of time was examined by secondary ion mass spectrometry and Rutherford backscattering spectrometry, giving evidence of a Ba redistribution against the interfacial region and an agglomeration of Cu within the film. While zero-resistivity temperatures of 1 mum thick films typically were between 80 and 88 K, magnetic characterization indicated weak coupling between the superconducting grains, resulting in low transport critical currents less-than-or-equal-to 10(3) A cm-2 at 77 K. The film properties of YBCO/sapphire were compared with those of YBCO processed in parallel on SrTiO3 or LaAlO3.